Electromagnetic interference immune tissue invasive system

ABSTRACT

An electromagnetic immune tissue invasive system includes a primary device housing. The primary device housing having a control circuit therein. A shielding is formed around the primary device housing to shield the primary device housing and any circuits therein from electromagnetic interference. A lead system transmits and receives signals between the primary device housing. The lead system is either a fiber optic system or an electrically shielded electrical lead system.

PRIORITY INFORMATION

[0001] This application claims priority from U.S. Provisional PatentApplication, Serial No. 60/269,817, filed on Feb. 20, 2001; the entirecontents of which are hereby incorporated by reference.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

[0002] The subject matter of co-pending U.S. patent application Ser. No.09/885,867, filed on Jun. 20, 2001, entitled “Controllable, WearableMRI-Compatible Cardiac Pacemaker With Pulse Carrying Photonic CatheterAnd VOO Functionality”; co-pending U.S. patent application Ser. No.09/885,868, filed on Jun. 20, 2001, entitled “Controllable, WearableMRI-Compatible Cardiac Pacemaker With Power Carrying Photonic CatheterAnd VOO Functionality”; co-pending U.S. patent application Ser. No.10/037,513, filed on Jan. 4, 2002, entitled “Optical Pulse Generator ForBattery Powered Photonic Pacemakers And Other Light Driven MedicalStimulation Equipment”; co-pending U.S. patent application Ser. No.10/037,720, filed on Jan. 4, 2002, entitled “Opto-Electric CouplingDevice For Photonic Pacemakers And Other Opto-Electric MedicalStimulation Equipment”; co-pending U.S. patent application Ser. No.09/943,216, filed on Aug. 30, 2001, entitled “Pulse width Cardiac PacingApparatus”; co-pending U.S. patent application Ser. No. 09/964,095,filed on Sep. 26, 2001, entitled “Process for Converting Light”; andco-pending U.S. patent application Ser. No. 09/921,066, filed on Aug. 2,2001, entitled “MRI-Resistant Implantable Device”. The entire contentsof each of the above noted co-pending U.S. patent applications (Ser.Nos: 09/885,867; 09/885,868; 10/037,513; 10/037,720; 09/943,216;09/964,095; and 09/921,066) are hereby incorporated by reference.

FIELD OF THE PRESENT INVENTION

[0003] The present invention relates generally to an implantable devicethat is immune or hardened to electromagnetic insult or interference.More particularly, the present invention is directed to implantablesystems that utilize fiber optic leads and other components to hardenedor immune the systems from electromagnetic insult, namelymagnetic-resonance imaging insult.

BACKGROUND OF THE PRESENT INVENTION

[0004] Magnetic resonance imaging (“MRI”) has been developed as animaging technique adapted to obtain both images of anatomical featuresof human patients as well as some aspects of the functional activitiesof biological tissue. These images have medical diagnostic value indetermining the state of the health of the tissue examined.

[0005] In an MRI process, a patient is typically aligned to place theportion of the patient's anatomy to be examined in the imaging volume ofthe MRI apparatus. Such an MRI apparatus typically comprises a primarymagnet for supplying a constant magnetic field (B₀) which, byconvention, is along the z-axis and is substantially homogeneous overthe imaging volume and secondary magnets that can provide linearmagnetic field gradients along each of three principal Cartesian axes inspace (generally x, y, and z, or x₁, x₂ and x₃, respectively). Amagnetic field gradient (ΔB₀/Δx_(i)) refers to the variation of thefield along the direction parallel to B₀ with respect to each of thethree principal Cartesian axes, x_(i). The apparatus also comprises oneor more RF (radio frequency) coils which provide excitation anddetection of the MRI signal.

[0006] The use of the MRI process with patients who have implantedmedical assist devices; such as cardiac assist devices or implantedinsulin pumps; often presents problems. As is known to those skilled inthe art, implantable devices (such as implantable pulse generators(IPGs) and cardioverter/defibrillator/pacemakers (CDPs)) are sensitiveto a variety of forms of electromagnetic interference (EMI) becausethese enumerated devices include sensing and logic systems that respondto low-level electrical signals emanating from the monitored tissueregion of the patient. Since the sensing systems and conductive elementsof these implantable devices are responsive to changes in localelectromagnetic fields, the implanted devices are vulnerable to externalsources of severe electromagnetic noise, and in particular, toelectromagnetic fields emitted during the magnetic resonance imaging(MRI) procedure. Thus, patients with implantable devices are generallyadvised not to undergo magnetic resonance imaging (MRI) procedures.

[0007] To more appreciate the problem, the use of implantable cardiacassist devices during a MRI process will be briefly discussed.

[0008] The human heart may suffer from two classes of rhythmic disordersor arrhythmias: bradycardia and tachyarrhythmia. Bradycardia occurs whenthe heart beats too slowly, and may be treated by a common implantablepacemaker delivering low voltage (about 3 V) pacing pulses.

[0009] The common implantable pacemaker is usually contained within ahermetically sealed enclosure, in order to protect the operationalcomponents of the device from the harsh environment of the body, as wellas to protect the body from the device.

[0010] The common implantable pacemaker operates in conjunction with oneor more electrically conductive leads, adapted to conduct electricalstimulating pulses to sites within the patient's heart, and tocommunicate sensed signals from those sites back to the implanteddevice.

[0011] Furthermore, the common implantable pacemaker typically has ametal case and a connector block mounted to the metal case that includesreceptacles for leads which may be used for electrical stimulation orwhich may be used for sensing of physiological signals. The battery andthe circuitry associated with the common implantable pacemaker arehermetically sealed within the case. Electrical interfaces are employedto connect the leads outside the metal case with the medical devicecircuitry and the battery inside the metal case.

[0012] Electrical interfaces serve the purpose of providing anelectrical circuit path extending from the interior of a hermeticallysealed metal case to an external point outside the case whilemaintaining the hermetic seal of the case. A conductive path is providedthrough the interface by a conductive pin that is electrically insulatedfrom the case itself.

[0013] Such interfaces typically include a ferrule that permitsattachment of the interface to the case, the conductive pin, and ahermetic glass or ceramic seal that supports the pin within the ferruleand isolates the pin from the metal case.

[0014] A common implantable pacemaker can, under some circumstances, besusceptible to electrical interference such that the desiredfunctionality of the pacemaker is impaired. For example, commonimplantable pacemaker requires protection against electricalinterference from electromagnetic interference (EMI), defibrillationpulses, electrostatic discharge, or other generally large voltages orcurrents generated by other devices external to the medical device. Asnoted above, more recently, it has become crucial that cardiac assistsystems be protected from magnetic-resonance imaging sources.

[0015] Such electrical interference can damage the circuitry of thecardiac assist systems or cause interference in the proper operation orfunctionality of the cardiac assist systems. For example, damage mayoccur due to high voltages or excessive currents introduced into thecardiac assist system.

[0016] Therefore, it is required that such voltages and currents belimited at the input of such cardiac assist systems, e.g., at theinterface. Protection from such voltages and currents has typically beenprovided at the input of a cardiac assist system by the use of one ormore zener diodes and one or more filter capacitors.

[0017] For example, one or more zener diodes may be connected betweenthe circuitry to be protected, e.g., pacemaker circuitry, and the metalcase of the medical device in a manner which grounds voltage surges andcurrent surges through the diode(s). Such zener diodes and capacitorsused for such applications may be in the form of discrete componentsmounted relative to circuitry at the input of a connector block wherevarious leads are connected to the implantable medical device, e.g., atthe interfaces for such leads.

[0018] However, such protection, provided by zener diodes and capacitorsplaced at the input of the medical device, increases the congestion ofthe medical device circuits, at least one zener diode and one capacitorper input/output connection or interface. This is contrary to the desirefor increased miniaturization of implantable medical devices.

[0019] Further, when such protection is provided, interconnect wirelength for connecting such protection circuitry and pins of theinterfaces to the medical device circuitry that performs desiredfunctions for the medical device tends to be undesirably long. Theexcessive wire length may lead to signal loss and undesirable inductiveeffects. The wire length can also act as an antenna that conductsundesirable electrical interference signals to sensitive CMOS circuitswithin the medical device to be protected.

[0020] Additionally, the radio frequency (RF) energy that is inductivelycoupled into the wire causes intense heating along the length of thewire, and at the electrodes that are attached to the heart wall. Thisheating may be sufficient to ablate the interior surface of the bloodvessel through which the wire lead is placed, and may be sufficient tocause scarring at the point where the electrodes contact the heart. Afurther result of this ablation and scarring is that the sensitive nodethat the electrode is intended to pace with low voltage signals becomesdesensitized, so that pacing the patient's heart becomes less reliable,and in some cases fails altogether.

[0021] Another conventional solution for protecting the implantablemedical device from electromagnetic interference is illustrated inFIG. 1. FIG. 1 is a schematic view of an implantable medical device 12embodying protection against electrical interference. At least one lead14 is connected to the implantable medical device 12 in connector blockregion 13 using an interface.

[0022] In the case where implantable medical device 12 is a pacemakerimplanted in a body 10, the pacemaker 12 includes at least one or bothof pacing and sensing leads represented generally as leads 14 to senseelectrical signals attendant to the depolarization and repolarization ofthe heart 16, and to provide pacing pulses for causing depolarization ofcardiac tissue in the vicinity of the distal ends thereof.

[0023]FIG. 2 more particularly illustrates the circuit that is usedconventionally to protect from electromagnetic interference. As shown inFIG. 2, protection circuitry 52 is provided using a diode arraycomponent 130. The diode array consists of five zener diode triggeredsemiconductor controlled rectifiers (SCRs) with anti-parallel diodesarranged in an array with one common connection. This allows for a smallfootprint despite the large currents that may be carried through thedevice during defibrillation, e.g., 10 amps. The SCRs 190-194 turn onand limit the voltage across the device when excessive voltage andcurrent surges occur.

[0024] As shown in FIG. 2, each of the zener diode triggered SCRs190-194 is connected to an electrically conductive pin 34-37,respectively. Further, each electrically conductive pin 34-37 isconnected to a medical device contact region 140-143 to be wire bondedto pads 90-93 of a printed circuit board. The diode array component 130is connected to the electrically conductive pins 34-37 via the diecontact regions 180-184, respectively, along with other electricalconductive traces of the printed circuit board.

[0025] Other attempts have been made to protect implantable devices fromMRI fields. For example, U.S. Pat. No. 5,968,083 (to Ciciarelli et al.)describes a device adapted to switch between low and high impedancemodes of operation in response to EMI insult. Furthermore, U.S. Pat. No.6,188,926 (to Vock) discloses a control unit for adjusting a cardiacpacing rate of a pacing unit to an interference backup rate when heartactivity cannot be sensed due to EMI.

[0026] Although, conventional medical devices provide some means forprotection against electromagnetic interference, these conventionaldevices require much circuitry and fail to provide fail-safe protectionagainst radiation produced by magnetic-resonance imaging procedures.Moreover, the conventional devices fail to address the possible damagethat can be done at the tissue interface due to RF-induced heating, andthey fail to address the unwanted heart stimulation that may result fromRF-induced electrical currents.

[0027] Thus, it is desirable to provide protection againstelectromagnetic interference, without requiring much circuitry and toprovide fail-safe protection against radiation produced bymagnetic-resonance imaging procedures. Moreover, it is desirable toprovide devices that prevent the possible damage that can be done at thetissue interface due to induced electrical signals and due to thermaltissue damage. Furthermore, it is desirable to provide to provide aneffective means for transferring energy from one point in the body toanother point without having the energy causing a detrimental effectupon the body.

SUMMARY OF THE PRESENT INVENTION

[0028] A first aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda lead system to transmit and receive signals between a heart and theprimary device housing.

[0029] A second aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a lead systemto transmit and receive signals between a heart and the primary devicehousing; and a detection circuit, located in the primary device housing,to detect an electromagnetic interference insult upon the cardiac assistsystem. The control circuit places the cardiac assist system in anasynchronous mode upon detection of the electromagnetic interferenceinsult by the detection system.

[0030] A third aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; afiber optic based lead system to receive signals at the primary housingfrom a heart; and an electrical based lead system to transmit signals tothe heart from the primary device housing.

[0031] A fourth aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda fiber optic based lead system to receive signals at the primaryhousing from a heart and to transmit signals to the heart from theprimary device housing.

[0032] A fifth aspect of the present invention is a cardiac assistsystem for implanting in a body of a patient, the cardiac assist systemcomprising; a main module; a magnetic-resonance imaging-immune auxiliarymodule; a communication channel between the main module and themagnetic-resonance imaging-immune auxiliary module for themagnetic-resonance imaging-immune auxiliary module to detect failure ofthe main module; and a controller for activating the magnetic-resonanceimaging-immune auxiliary module upon detection of failure of the mainmodule.

[0033] A sixth aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housingincluding a power supply and a light source; the primary device housinghaving a control circuit therein; a shielding formed around the primarydevice housing to shield the primary device housing and any circuitstherein from electromagnetic interference; a cardiac assist deviceassociated with a heart; and a photonic lead system to transmit betweenthe primary device housing and the cardiac assist device, both power andcontrol signals in the form of light.

[0034] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a first control circuit, therein, toperform synchronous cardiac assist operations; a secondary devicehousing having a second control circuit therein, to perform asynchronouscardiac assist operations; and a detection circuit, communicativelycoupled to the first and second control circuits, to detect anelectromagnetic interference insult upon the cardiac assist system. Thefirst control circuit terminates synchronous cardiac assist operationsand the second control circuit initiates asynchronous cardiac assistoperations upon detection of the electromagnetic interference insult bythe detection system.

[0035] A further aspect of the present invention is an implantable cablefor transmission of a signal to and from a body tissue of a vertebrate.The implantable cable includes a fiber optic bundle having a surface ofnon-immunogenic, physiologically compatible material, the fiber opticbundle being capable of being permanently implanted in a body cavity orsubcutaneously, the fiber optic bundle having a distal end forimplantation at or adjacent to the body tissue and a proximal end. Theproximal end is adapted to couple to and direct an optical signalsource; the distal end is adapted to couple to an optical stimulator.The fiber optic bundle delivers an optical signal intended to cause anoptical simulator located at the distal end to deliver an excitatorystimulus to a selected body tissue, the stimulus being causing theselected body tissue to function as desired.

[0036] A further aspect of the present invention is an implantable cablefor transmission of a signal to and from a body tissue of a vertebrate.The implantable cable includes a fiber optic bundle having a surface ofnon-immunogenic, physiologically compatible material, the fiber opticbundle being capable of being permanently implanted in a body cavity orsubcutaneously, the fiber optic bundle having a distal end forimplantation at or adjacent to the body tissue and a proximal end. Theproximal end is adapted to couple to an optical signal receiver, thedistal end is adapted to couple to a sensor; the fiber optic bundledelivers an optical signal from a coupled sensor intended to cause anoptical signal receiver coupled to the proximal end to monitorcharacteristics of a selected body tissue.

[0037] A further aspect of the present invention is an implantable cablefor transmission of power to a body tissue of a vertebrate. Theimplantable cable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a proximal end adapted to couple to an opticalportal, a coupled optical portal being able to receive light from asource external to the vertebrate, and a distal end adapted to couple toa photoelectric receiver, a coupled photoelectric receiver being able toconvert light into electrical energy for use at the distal end.

[0038] A further aspect of the present invention is an implantable cablefor the transmission of power to a body tissue of a vertebrate. Theimplantable cable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a distal end adapted to couple to a sensor, acoupled sensor being able to produce light signal based on a measuredcharacteristic of a selected body tissue region, and a proximal endbeing adapted to couple to an optical portal, the optical portal beingable to receive light produced by a coupled sensor.

[0039] A further aspect of the present invention is an implantable cablefor the transmission of power to a body tissue of a vertebrate. Theimplantable cable consists of a fiber optic lead having a surface ofnon-immunogenic, physiologically compatible material and being capableof being permanently implanted in a body cavity or subcutaneously. Thefiber optic lead has a proximal end being adapted to be coupled to anoptical portal, a coupled optical portal being able to receive lightfrom a light source, and a distal end being adapted to be coupled to aphotoelectric receiver, a coupled photoelectric receiver being able toconvert light into electrical energy for use at the distal end.

[0040] A further aspect of the present invention is an implantable cablefor the transmission of power to a body tissue of a vertebrate. Theimplantable cable includes a fiber optic lead having a cylindricalsurface of non-immunogenic, physiologically compatible material andbeing capable of being permanently implanted in a body cavity orsubcutaneously. The fiber optic lead has a proximal end coupled to anelectro-optical source; the electro-optical source converts electricalenergy into light energy. The distal end coupled to a photoelectricreceiver, the photoelectric receiver converts light energy intoelectrical energy for use at the distal end.

[0041] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing,having a control circuit therein, and a fiber optic based communicationsystem to transmit and receive signals between a desired anatomicalcardiac tissue region and the primary device housing.

[0042] A still further aspect of the present invention is a tissueinvasive device. The tissue invasive device includes a primary devicehousing, having a control circuit therein and a fiber optic basedcommunication system to transmit and receive signals between a selectedtissue region and the primary device housing.

[0043] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing,having a control circuit therein, and a lead system to transmit andreceive signals between a desired anatomical cardiac tissue region andthe primary device housing. The lead system includes a sensing andstimulation system at an epicardial-lead interface with the desiredanatomical cardiac tissue region. The sensing and stimulation systemincludes optical sensing components to detect physiological signals fromthe desired anatomical cardiac tissue region.

[0044] A still further aspect of the present invention is a tissueinvasive device. The tissue invasive device includes a primary devicehousing, having a control circuit therein, and a lead system to transmitand receive signals between a selected tissue region and the primarydevice housing. The lead system includes a sensing and stimulationsystem at an interface with the selected tissue region. The sensing andstimulation system includes optical sensing components to detectphysiological signals from the selected tissue region.

[0045] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing,having a control circuit therein, and a lead system to transmit andreceive signals between a desired anatomical cardiac tissue region andthe primary device housing. The lead system includes a sensing andstimulation system at an epicardial-lead interface with the desiredanatomical cardiac tissue region; the sensing and stimulation systemincludes optical sensing components to detect physiological signals fromthe desired anatomical cardiac tissue region and electrical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

[0046] A still further aspect of the present invention is a tissueinvasive device. The tissue invasive device includes a primary devicehousing, having a control circuit therein, and a lead system to transmitand receive signals between a selected tissue region and the primarydevice housing. The lead system includes a sensing and stimulationsystem at an epicardial-lead interface with the selected tissue region.The sensing and stimulation system includes optical sensing componentsto detect physiological signals from the selected tissue region andelectrical sensing components to detect physiological signals from theselected tissue region.

[0047] A further aspect of the present invention is a transducer systemto transmit and receive signals between a selected tissue region and atissue invasive device. The transducer system consists of an electricallead and an electrode located on an end of the electrical lead having ananti-antenna geometrical shape, the anti-antenna geometrical shapepreventing the electrode from picking up and conducting strayelectromagnetic interference.

[0048] A further aspect of the present invention is a cardiac assisttransducer system to transmit and receive signals between a cardiactissue region and a cardiac assist device. The cardiac assist transducersystem consists of an electrical lead to deliver electrical pulses tothe cardiac tissue region; and an electrode located on an end of theelectrical lead having an anti-antenna geometrical shape, theanti-antenna geometrical shape preventing the electrode from picking upand conducting stray electromagnetic interference.

[0049] A still further aspect of the present invention is a cardiacassist system. The cardiac assist system consists of a primary devicehousing; the primary device housing has a control circuit therein; alead system to transmit and receive signals between a heart and theprimary device housing; a shielding formed around the lead system toshield the lead system from electromagnetic interference; and abiocompatible material formed around the shielding.

[0050] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing;the primary device housing has a control circuit therein; a fiber opticEMI-immune lead system to transmit and receive signals between a heartand the primary device housing; and a biocompatible material formedaround the fiber optic EMI-immune lead system.

[0051] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing;the primary device housing has a control circuit therein; anoptical-electrical lead system to transmit and receive signals between aheart and the primary device housing; a shielding formed around theoptical-electrical lead system to shield the optical-electrical leadsystem from electromagnetic interference; and a biocompatible materialformed around the shielding.

[0052] A further aspect of the present invention is a tissue invasivedevice. The tissue invasive device consists of a primary device housing;the primary device housing has a control circuit therein; a lead systemto transmit and receive signals between a selected tissue region and theprimary device housing; a shielding formed around the lead system toshield the lead system from electromagnetic interference; and abiocompatible material formed around the shielding.

[0053] A still further aspect of the present invention is a tissueinvasive device. The tissue invasive device consists of a primary devicehousing; the primary device housing having a control circuit therein; afiber optic EMI-immune lead system to transmit and receive signalsbetween a selected tissue region and the primary device housing; and abiocompatible material formed around the fiber optic EMI-immune leadsystem.

[0054] A further aspect of the present invention is a tissue invasivedevice. The tissue invasive device consists of a primary device housing;the primary device housing having a control circuit therein; anoptical-electrical lead system to transmit and receive signals between aselected tissue region and the primary device housing; a shieldingformed around the optical-electrical lead system to shield theoptical-electrical lead system from electromagnetic interference; and abiocompatible material formed around the shielding.

[0055] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing;the primary device housing has a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda biocompatible material formed around the shielding.

[0056] A further aspect of the present invention is a tissue invasivedevice. The tissue invasive device consists of a primary device housing;the primary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda biocompatible material formed around the shielding.

[0057] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housing;the primary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; abiocompatible material formed around the shielding; and a detectioncircuit, located in the primary device housing, to detect anelectromagnetic interference insult upon the cardiac assist system. Thecontrol circuit will place the cardiac assist system in an asynchronousmode upon detection of the electromagnetic interference insult by thedetection system.

[0058] A still further aspect of the present invention is a tissueinvasive device. The tissue invasive device consists of a primary devicehousing; the primary device housing has a control circuit thereinoperating in a first mode. A shielding formed around the primary devicehousing to shield the primary device housing and any circuits thereinfrom electromagnetic interference; a biocompatible material formedaround the shielding; and a detection circuit, located in the primarydevice housing, to detect an electromagnetic interference insult uponthe tissue invasive device. The control circuit places the tissueinvasive device in a second mode upon detection of the electromagneticinterference insult by the detection system.

[0059] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system consists of a primary device housinghaving a first control circuit, therein, to perform synchronous cardiacassist operations; a first shielding formed around the primary device,housing to shield the primary device housing and any circuits thereinfrom electromagnetic interference; a first biocompatible material formedaround the first shielding; a secondary device housing having a secondcontrol circuit, therein, to perform asynchronous cardiac assistoperations; a second shielding formed around the secondary devicehousing to shield the secondary device housing and any circuits thereinfrom electromagnetic interference; a second biocompatible materialformed around the second shielding; and a detection circuit,communicatively coupled to the first and second control circuits, todetect an electromagnetic interference insult upon the cardiac assistsystem. The first control circuit terminates synchronous cardiac assistoperations and the second control circuit initiates asynchronous cardiacassist operations upon detection of the electromagnetic interferenceinsult by the detection system.

[0060] A still further aspect of the present invention is a cardiacassist system for implanting in a body of a patient. The cardiac assistsystem consists of a main module; a first shielding formed around themain module to shield the main module and any circuits therein frommagnetic-resonance imaging interference; a first biocompatible materialformed around the first shielding; a magnetic-resonance imaging-immuneauxiliary module; a second shielding formed around themagnetic-resonance imaging-immune auxiliary module to shield themagnetic-resonance imaging-immune auxiliary module and any circuitstherein from magnetic-resonance imaging interference; a secondbiocompatible material formed around the second shielding; acommunication channel between the main module and the magnetic-resonanceimaging-immune auxiliary module for the magnetic-resonanceimaging-immune auxiliary module to detect failure of the main module;and a controller for activating the magnetic-resonance imaging-immuneauxiliary module upon detection of failure of the main module.

[0061] A further aspect of the present invention is a cardiac assistsystem for implanting in the body of a patient. The cardiac assistsystem consists of a main module; a first biocompatible material formedaround the main module; an magnetic-resonance imaging-hardened auxiliarymodule; a shielding formed around the magnetic-resonanceimaging-hardened auxiliary module to shield the magnetic-resonanceimaging-hardened auxiliary module and any circuits therein frommagnetic-resonance imaging interference; a second biocompatible materialformed around the second shielding; and a communication channel betweenthe main module and the magnetic-resonance imaging-hardened auxiliarymodule. The magnetic-resonance imaging-hardened auxiliary moduledetecting, through the communication channel, failure of the mainmodule; the magnetic-resonance imaging-hardened auxiliary moduleincluding a controller for activating the magnetic-resonanceimaging-hardened auxiliary module upon detection of failure of the mainmodule.

[0062] A further aspect of the present invention is a cardiac assistdevice. The cardiac assist device consists of a primary device housing;the primary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a selected cardiactissue region and the primary device housing; a switch to place thecontrol circuitry into a fixed-rate mode of operation; an acousticsensor to sense a predetermined acoustic signal. The switch places thecontrol circuitry into a fixed-rate mode of operation when the acousticsensor senses the predetermined acoustic signal.

[0063] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a selected cardiactissue region and the primary device housing; a switch to place thecontrol circuitry into a fixed-rate mode of operation; a near infraredsensor to sense a predetermined near infrared signal; the switch placingthe control circuitry into a fixed-rate mode of operations when the nearinfrared sensor senses the predetermined near infrared signal.

[0064] A still further aspect of the present invention is an implantablecable for the transmission of signals to and from a body tissue of avertebrate. The implantable cable consists of a fiber optic lead havinga surface of non-immunogenic, physiologically compatible material andbeing capable of being permanently implanted in a body cavity orsubcutaneously; the fiber optic lead having a distal end forimplantation at or adjacent to the body tissue and a proximal end; thefiber optic lead including a first optical fiber and a second opticalfiber; the first optical fiber having, a proximal end coupled to anoptical signal source, and a distal end coupled to an opticalstimulator. The optical signal source generating an optical signalintended to cause the optical stimulator located at a distal end todeliver an excitatory stimulus to a selected body tissue, the stimuluscausing the selected body tissue to function as desired. The secondoptical fiber having a distal end coupled to a sensor, and a proximalend coupled to a device responsive to an optical signal delivered by thesecond optical fiber; the sensor generating an optical signal torepresent a state of a function of the selected body tissue to providefeedback to affect the activity of the optical signal source.

[0065] A further aspect of the present invention is an implantable cablefor the transmission of signals to and from a body tissue of avertebrate. The implantable cable includes a fiber optic lead having asurface of non-immunogenic, physiologically compatible material andbeing capable of being permanently implanted in a body cavity orsubcutaneously; the fiber optic lead having a distal end forimplantation at or adjacent to the body tissue and a proximal end; theproximal end of the fiber optic lead being coupled to an optical signalsource and an optical device. The distal end of the fiber optic leadbeing coupled to an optical stimulator and a sensor; the optical signalsource generating an optical signal intended to cause the opticalstimulator located at a distal end to deliver an excitatory stimulus toa selected body tissue, the stimulus being causing the selected bodytissue to function as desired. The optical device being responsive to anoptical signal generated by the sensor, the optical signal generated bythe sensor rep representing a state of a function of the selected bodytissue to provide feedback to affect the activity of the optical signalsource.

[0066] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housingincluding a power supply and a light source; the primary device housinghaving a control circuit therein; a shielding formed around the primarydevice housing to shield the primary device housing and any circuitstherein from electromagnetic interference; a cardiac assist deviceassociated with a heart; a photonic lead system to transmit between theprimary device housing and the cardiac assist device, both power andcontrol signals in the form of light; a photoresponsive device toconvert the light transmitted by the photonic lead system intoelectrical energy and to sense variations in the light energy to producecontrol signals; a charge accumulating device to receive and store theelectrical energy produced by the photoresponsive device; and adischarge control device, responsive to the control signals, to directthe stored electrical energy from the charge accumulating device to thecardiac assist device associated with the heart.

[0067] A further aspect of the present invention is a tissue implantabledevice. The tissue implantable device includes a primary device housingincluding a power supply and a light source; the primary device housinghaving a control circuit therein; a shielding formed around the primarydevice housing to shield the primary device housing and any circuitstherein from electromagnetic interference; a tissue interface deviceassociated with a distinct tissue region; a photonic lead system totransmit between the primary device housing and the tissue interfacedevice, both power and control signals in the form of light; aphotoresponsive device to convert the light transmitted by the photoniclead system into electrical energy and to sense variations in the lightenergy to produce control signals; a discharge control device,responsive to the control signals, to direct the stored electricalenergy from the charge accumulating device to the tissue interfacedevice associated with a distinct tissue region.

[0068] A further aspect of the present invention is a tissue implantabledevice. The tissue implantable device includes a primary device housing;the primary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a tissue region ofconcern and the primary device housing; and a detection circuit todetect a phase timing of an external electromagnetic field; the controlcircuit altering its operations to avoid interfering with the detectedexternal electromagnetic field.

[0069] A still further aspect of the present invention is a method forpreventing a tissue implantable device failure during magnetic resonanceimaging. The method includes determining a quiet period for a tissueimplantable device and generating a magnetic resonance imaging pulseduring a quiet period of the tissue implantable device.

[0070] A further aspect of the present invention is a method forpreventing a tissue implantable device failure due to an externalelectromagnetic field source. The method includes detecting a phasetiming of an external electromagnetic field and altering operations ofthe tissue implantable device to avoid interfering with the detectedexternal electromagnetic field.

[0071] A further aspect of the present invention is a method forpreventing a tissue implantable device failure during magnetic resonanceimaging. The method includes detecting a phase timing of an externalmagnetic resonance imaging pulse field and altering operations of thetissue implantable device to avoid interfering with the detectedexternal magnetic resonance imaging pulse field.

[0072] A further aspect of the present invention is a cardiac assistsystem for implanting in the body of a patient. The cardiac assistsystem includes a main module; an magnetic-resonance imaging-hardenedauxiliary module; and a communication channel between the main moduleand the magnetic-resonance imaging-hardened auxiliary module; themagnetic-resonance imaging-hardened auxiliary module detecting, throughthe communication channel, failure of the main module; themagnetic-resonance imaging-hardened auxiliary module including acontroller for activating the auxiliary module upon detection of failureof the main module.

[0073] A further aspect of the present invention is a signaling systemfor a two-module implantable medical device having a main module and anauxiliary module. The signaling system consists of signaling means inthe main module for generating a signal to the auxiliary module, thesignal representing a status of the main module or an instruction forthe auxiliary module to activate; sensing means in the auxiliary module,in response to the signal from the signaling means, for determining ifthe auxiliary module should activate; and a switch to activate theauxiliary module when the sensing means determines that the signal fromthe signaling means indicates that the auxiliary module should activate.

[0074] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing; theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; anda lead system to transmit and receive signals between a heart and theprimary device housing; the control circuitry including an oscillatorand amplifier operating at an amplitude level above that of an inducedsignal from a magnetic-resonance imaging field.

[0075] A still further aspect of the present invention is a cardiacassist system. The cardiac assist system includes a primary devicehousing; the primary device housing having a control circuit therein; ashielding formed around the primary device housing to shield the primarydevice housing and any circuits therein from electromagneticinterference; a lead system to transmit and receive signals between aheart and the primary device housing; a switch to place the controlcircuitry into a fixed-rate mode of operation; a changing magnetic fieldsensor to sense a change in magnetic field around the primary housing,the switch placing the control circuitry into a fixed-rate mode ofoperation when the changing magnetic field sensor senses a predeterminedencoded changing magnetic field.

[0076] A further aspect of the present invention is an electromagneticradiation immune tissue invasive delivery system. The electromagneticradiation immune tissue invasive delivery system includes a photoniclead having a proximal end and a distal end; a storage device, locatedat the proximal end of the photonic lead, to store a therapeuticsubstance to be introduced into a tissue region; a delivery device todelivery a portion of the stored therapeutic substance to a tissueregion; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength and a second lighthaving a second wavelength; a wave-guide between the proximal end anddistal end of the photonic lead; a bio-sensor, in the distal end of thephotonic lead, to sense characteristics of a predetermined tissueregion; a distal sensor, in the distal end of the photonic lead, toconvert the first light into electrical energy and, responsive to thebio-sensor, to reflect the second light back the proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region; a proximal sensor, in the proximal end of the photoniclead, to convert the modulated second light into electrical energy; anda control circuit, in response to the electrical energy from theproximal sensor, to control an amount of the stored therapeuticsubstance to be introduced into the tissue region.

[0077] A further aspect of the present invention is an electromagneticradiation immune tissue invasive delivery system. The electromagneticradiation immune tissue invasive delivery system includes a photoniclead having a proximal end and a distal end; a storage device, locatedat the proximal end of the photonic lead, to store a therapeuticsubstance to be introduced into a tissue region; a delivery device todeliver a portion of the stored therapeutic substance to a tissueregion; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength and a second lighthaving a second wavelength; a wave-guide between the proximal end anddistal end of the photonic lead; a bio-sensor, in the distal end of thephotonic lead, to sense characteristics of a predetermined tissueregion; a distal sensor, in the distal end of the photonic lead, toconvert the first light into electrical energy and, responsive to thebio-sensor, to emit a second light having a second wavelength toproximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristics of thepredetermined tissue region; a proximal sensor, in the proximal end ofthe photonic lead, to convert the modulated second light into electricalenergy; and a control circuit, in response to the electrical energy fromthe proximal sensor, to control an amount of the stored therapeuticsubstance to be introduced into the tissue region.

[0078] A further aspect of the present invention is an electromagneticradiation immune tissue invasive stimulation system. The electromagneticradiation immune tissue invasive stimulation system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength; a wave-guide between the proximal end and distal endof the photonic lead; a distal sensor, in the distal end of the photoniclead, to convert the first light into electrical energy into controlsignals; an electrical energy storage device to store electrical energy;and a control circuit, in response to the control signals, to cause aportion of the stored electrical energy to be delivered to apredetermined tissue region.

[0079] A further aspect of the present invention is an electromagneticradiation immune tissue invasive sensing system. The electromagneticradiation immune tissue invasive sensing system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a distal sensor, in the distal end of the photonic lead,to convert the first light into electrical energy into control signals;an electrical energy storage device to store electrical energy; and abio-sensor, in the distal end of the photonic lead, to sense acharacteristic of a predetermined tissue region. The light source, inthe proximal end of the photonic lead, produces a second light having asecond wavelength. The distal sensor, in the distal end of the photoniclead and responsive to the bio-sensor, reflects the second light backthe proximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristic of thepredetermined tissue region.

[0080] A still further aspect of the present invention is anelectromagnetic radiation immune tissue invasive sensing system. Theelectromagnetic radiation immune tissue invasive sensing system includesa photonic lead having a proximal end and a distal end; a light source,in the proximal end of the photonic lead, to produce a first lighthaving a first wavelength and a second light having a second wavelength;a wave-guide between the proximal end and the distal end of the photoniclead; a bio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal sensor,in the distal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region.

[0081] A further aspect of the present invention is an electromagneticradiation immune tissue invasive sensing system. The electromagneticradiation immune tissue invasive sensing system includes a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength; a wave-guide between the proximal end and distal end of thephotonic lead; a bio-sensor, in the distal end of the photonic lead, tosense characteristics of a predetermined tissue region; and a distalsensor, in the distal end of the photonic lead, to convert the firstlight into electrical energy and, responsive to the bio-sensor, to emita second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

[0082] A further aspect of the present invention is a photonic leadsystem. The photonic lead system includes a photonic lead having adistal end and a proximal end; and a magnetic radiation coil, located inthe distal end, to detect characteristics of magnetic radiation of apredetermined nature.

[0083] A still further aspect of the present invention is anelectromagnetic radiation immune sensing system. The electromagneticradiation immune sensing system includes a photonic lead having aproximal end and a distal end; a light source, in the proximal end ofthe photonic lead, to produce a first light having a first wavelengthand a second light having a second wavelength; a wave-guide between theproximal end and distal end of the photonic lead; a biosensor, in thedistal end of the photonic lead, to measure changes in an electric fieldlocated outside a body, the electric field being generated by theshifting voltages on a body's skin surface; and a distal sensor, in thedistal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the measuredchanges in the electric field.

[0084] A further aspect of the present invention is an electromagneticradiation immune sensing system. The electromagnetic radiation immunesensing system includes a photonic lead having a proximal end and adistal end; a light source, in the proximal end of the photonic lead, toproduce a first light having a first wavelength; a wave-guide betweenthe proximal end and distal end of the photonic lead; a bio-sensor, inthe distal end of the photonic lead, to, measure changes in an electricfield located outside a body, the electric field being generated by theshifting voltages on a body's skin surface; and a distal sensor, in thedistal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to emit a secondlight having a second wavelength to proximal end of the photonic leadsuch that a characteristic of the second light is modulated to encodethe measured changes in the electric field.

[0085] A further aspect of the present invention is a cardiac assistsystem. The cardiac assist system includes a primary device housing, theprimary device housing having a control circuit therein; a shieldingformed around the primary device housing to shield the primary devicehousing and any circuits therein from electromagnetic interference; alead system to transmit and receive signals between a heart and theprimary device housing; a switch to place the control circuitry into afixed-rate mode of operation; and a changing magnetic field sensor tosense a change in magnetic field around the primary housing. The switchcauses the control circuitry to turn-off and cease operation when thechanging magnetic field sensor senses a predetermined encoded changingmagnetic field.

[0086] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a radiationscattering medium at the distal end of the photonic lead to receiveradiation from the wave-guide; and a plurality of sensors to receivescattered radiation from the radiation scattering medium and convert thereceived scattered radiation into electrical energy.

[0087] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a first wave-guidebetween the proximal end and distal end of the photonic lead; a secondwave-guide, having a plurality of beam splitters therein at the distalend of the photonic lead to receive radiation from the first wave-guide;and a plurality of sensors to receive radiation from the beam splittersin the second wave-guide and convert the received radiation intoelectrical energy.

[0088] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; and a plurality ofstacked sensors to receive radiation from the wave-guide and convert thereceived radiation into electrical energy. Each sensor absorbs afraction of radiation incident upon the stack of sensors.

[0089] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; and a plurality ofconcentric sensors to receive radiation from the wave-guide and convertthe received radiation into electrical energy. Each concentric sensorsabsorbs a fraction of radiation from said wave-guide.

[0090] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; and a plurality of switchable capacitorsconnected in parallel to an output of the sensor to enable simultaneouscharging of the capacitors.

[0091] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; a control circuit connected to an output of thesensor; and a plurality of switchable capacitors connected to thecontrol circuit.

[0092] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a photonic lead having a proximal end and a distal end; a lightsource, at the proximal end of the photonic lead; a wave-guide betweenthe proximal end and distal end of the photonic lead; a sensor toreceive radiation from the wave-guide and convert the received radiationinto electrical energy; and a plurality of switchable capacitorsconnected to an output of the sensor to enable sequential charging ofthe capacitors with a pre-determined pulse intensity and duration.

[0093] A further aspect of the present invention is an electromagneticradiation immune tissue invasive energy transfer system. Theelectromagnetic radiation immune tissue invasive energy transfer systemincludes a light source; a radiation beam splitter having multiple beamsplitters; a plurality of wave-guides, each wave-guide receivingradiation from a beam splitter; and a plurality of sensors, each sensorreceiving radiation from one of the plurality of wave-guides to convertthe received radiation into electrical energy.

[0094] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; awave-guide between the proximal end and distal end of the photonic lead;a radiation scattering medium at the distal end of the photonic lead toreceive radiation from the wave-guide; a plurality of power sensors toreceive scattered radiation from the radiation scattering medium andconvert the received scattered radiation into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

[0095] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; a firstwave-guide between the proximal end and distal end of the photonic lead;a second wave-guide, having a plurality of power beam splitters thereinat the distal end of the photonic lead to receive and reflect the firstlight from the first wave-guide; a plurality of power sensors to receivethe first light from the power beam splitters in the second wave-guideand convert the received first light into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

[0096] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; awave-guide between the proximal end and distal end of the photonic lead;a plurality of power sensors to receive the first light from thewave-guide and convert the received first light into electrical energy,each power sensor absorbing a fraction of the received first light; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; and a distal emitter,in the distal end of the photonic lead and responsive to the bio-sensor,to emit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region.

[0097] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; awave-guide between the proximal end and distal end of the photonic lead;a bio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a distal emitter, inthe distal end of the photonic lead and responsive to the bio-sensor, toemit a second light having a second wavelength to proximal end of thephotonic lead such that a characteristic of the second light ismodulated to encode the sensed characteristics of the predeterminedtissue region; a power sensor to receive the first light from thewave-guide and convert the received first light into electrical energy;and a plurality of switchable capacitors operatively connected to anoutput of the power sensor.

[0098] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; awave-guide between the proximal end and distal end of the photonic lead;a radiation scattering medium at the distal end of the photonic lead toreceive radiation from the wave-guide; a plurality of power sensors toreceive scattered radiation from the radiation scattering medium andconvert the received scattered radiation into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a distal sensor, inthe distal end of the photonic lead, responsive to the bio-sensor, toreflect the second light back to the proximal end of the photonic leadsuch that a characteristic of the second light is modulated to encodethe sensed characteristics of the predetermined tissue region; and abeam splitter to direct the second light to the distal sensor.

[0099] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; a firstwave-guide between the proximal end and distal end of the photonic lead;a second wave-guide, having a plurality of power beam splitters thereinat the distal end of the photonic lead to receive and reflect the firstlight from the first wave-guide; a plurality of power sensors to receivethe first light from the power beam splitters in the second wave-guideand convert the received first light into electrical energy; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a sensor beam splitterto reflect the second light from the first wave-guide; and a distalsensor, in the distal end of the photonic lead, responsive to thebio-sensor, to receive the second light from the sensor beam splitterand to reflect the second light back to the proximal end of the photoniclead such that a characteristic of the second light is modulated toencode the sensed characteristics of the predetermined tissue region.

[0100] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system a photonic leadhaving a proximal end and a distal end; a light source, in the proximalend of the photonic lead, to produce a first light having a firstwavelength and a second light having a second wavelength; a wave-guidebetween the proximal end and distal end of the photonic lead; aplurality of power sensors to receive the first light from thewave-guide and convert the received first light into electrical energy,each power sensor absorbing a fraction of the received first light; abio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a sensor beam splitterto reflect the second light from the wave-guide; and a distal sensor, inthe distal end of the photonic lead, responsive to the bio-sensor, toreceive the second light from the sensor beam splitter and to reflectthe second light back to the proximal end of the photonic lead such thata characteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region.

[0101] A further aspect of the present invention is a tissue invasivephotonic system. The tissue invasive photonic system includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength and a second light having a second wavelength; awave-guide between the proximal end and distal end of the photonic lead;a bio-sensor, in the distal end of the photonic lead, to sensecharacteristics of a predetermined tissue region; a sensor beam splitterto reflect the second light from the wave-guide; a distal sensor, in thedistal end of the photonic lead, responsive to the bio-sensor, toreceive the second light from the sensor beam splitter and to reflectthe second light back to the proximal end of the photonic lead such thata characteristic of the second light is modulated to encode the sensedcharacteristics of the predetermined tissue region; a power sensor toreceive the first light from the wave-guide and convert the receivedfirst light into electrical energy; and a plurality of switchablecapacitors operatively connected to an output of the power sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0102] The present invention may take form in various components andarrangements of components, and in various steps and arrangements ofsteps. The drawings are only for purposes of illustrating a preferredembodiment and are not to be construed as limiting the presentinvention, wherein:

[0103]FIGS. 1 and 2 are illustrations of conventional techniques used toprotect against electromagnetic interference;

[0104]FIG. 3 is a block diagram of one embodiment of a MRI immunecardiac assist system according to some or all of the concepts of thepresent invention;

[0105]FIG. 4 is a block diagram of another embodiment of a MRI immunecardiac assist system according to some or all of the concepts of thepresent invention;

[0106]FIGS. 5 through 20 are schematics of various optical sensingdevices according to some or all of the concepts of the presentinvention;

[0107]FIG. 21 illustrates a pressure optical transducer according tosome or all of the concepts of the present invention;

[0108]FIGS. 22 through 26 are block diagrams of various pressure opticaltransducers according to some or all of the concepts of the presentinvention;

[0109]FIG. 27 is a partial view of a cardiac assist device according tosome or all of the concepts of the present invention with anintermediate portion of the photonic catheter thereof removed forillustrative clarity;

[0110]FIG. 28 is an enlarged partial perspective view of componentslocated at the distal end of the photonic catheter FIG. 27;

[0111]FIG. 29 is a detailed partial schematic view showing oneconstruction of an electro-optical transducer according to some or allof the concepts of the present invention;

[0112]FIG. 31 is a graph depicting a typical pulse sequence used inpacing a human heart, over an interval equivalent to a nominal 1 Hzhuman heartbeat;

[0113]FIG. 32 is a similar graph depicting the pacing pulse as shown inFIG. 31, but with a much finer time scale;

[0114]FIG. 33 is a schematic representation of a cardiac pacing leadwith two electrodes;

[0115]FIG. 34 is a schematic representation of a similar cardiac pacinglead with three electrodes;

[0116]FIG. 35 is a schematic representation of yet another cardiacpacing lead with two pairs of electrodes;

[0117]FIG. 36 is a graph depicting the use of pulsewidth pacing signalsand interleaved periods for sensing heart activity;

[0118]FIG. 37 is a graph depicting the operation of one embodimentaccording to some or all of the concepts of the present invention thatgains energy efficiency by means of early termination of the pacingsignal;

[0119]FIG. 38 is a graph depicting the operation of another embodimentaccording to some or all of the concepts of the present invention thatgains energy efficiency by means of both early termination of the pacingsignal and by gradient pulsewidth power control;

[0120]FIG. 39 is another graph of the embodiment in FIG. 38, but withalternate waveform of the pacing signal;

[0121]FIGS. 40 through 42 are schematic circuit diagrams of a pulsegenerator according to some or all of the concepts of the presentinvention;

[0122]FIG. 43 is a schematic circuit diagram showing one embodiment ofan opto-electric coupling device according to some or all of theconcepts of the present invention;

[0123]FIGS. 44 and 45 are graphical illustrations of pulse waveformsthat may be, respectively, input to and output from the opto-electriccoupling device according to some or all of the concepts of the presentinvention;

[0124]FIG. 46 is a schematic circuit diagram showing a second embodimentof an opto-electric coupling device in accordance with the invention;

[0125]FIG. 47 is a schematic circuit diagram showing a constant currentregulator for a laser light generator according to some or all of theconcepts of the present invention;

[0126]FIG. 48 is a detailed partial schematic view showing oneconstruction of an electro-optical transducer according to some or allof the concepts of the present invention;

[0127]FIG. 49 is a schematic circuit diagram of a pulse generatoraccording to some or all of the concepts of the present invention;

[0128]FIG. 50 is an exploded perspective view of a hermetic componenthousing according to some or all of the concepts of the presentinvention;

[0129]FIGS. 51 through 53 are sectional axial centerline views showingalternative ways in which the component housing of FIG. 50 can beconfigured;

[0130]FIG. 54 is a perspective view of the component housing of FIG. 50showing details of exemplary components that may be housed therein;

[0131]FIG. 55 is a partial exploded perspective view of a hermeticcomponent housing according to some or all of the concepts of thepresent invention;

[0132]FIGS. 56 and 57 are sectional axial centerline views showingalternative ways in which the component housing of FIG. 55 can beconfigured;

[0133]FIG. 58 is a perspective view of the component housing of FIG. 55showing details of exemplary components that may be housed therein;

[0134]FIG. 59 is a partially exploded perspective view of a hermeticcomponent housing according to some or all of the concepts of thepresent invention;

[0135]FIG. 60 is a sectional view taken along the axial centerline ofthe component housing of FIG. 59;

[0136]FIG. 61 is a perspective view of the component housing of FIG. 59showing details of exemplary components that may be housed therein; and

[0137]FIGS. 62 through 65 are schematics of various optical pressuretransducers according to some or all of the concepts of the presentinvention;

[0138]FIGS. 66 through 69 are schematics of various MRI coils for aphotonic catheter according to some or all of the concepts of thepresent invention; and

[0139]FIGS. 70 through 85 are schematics of various optical powertransfer devices according to some or all of the concepts of the presentinvention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0140] As noted above, the present invention is directed to animplantable device that is immune or hardened to electromagnetic insultor interference.

[0141]FIG. 3 illustrates a cardiac assist system that is immune orhardened electromagnetic insult or interference, namely to magneticradiation imaging, MRI. As illustrated in FIG. 3, a main module 40includes a processor circuit 43 that controls the operations of thecardiac assist system. The processor unit 43 provides control signals toa pacing unit 45. The pacing unit 45 produces packets of energy tostimulate the heart 49 to start beating or to beat at a predeterminedrate or pace. The processor circuit 43 also receives information aboutthe conditions of the heart 49 from a sensing unit 44. The sensing unit44, through sensors or electrodes, monitors the conditions of the heart49 to provide feedback information to the processor circuit 43.

[0142] A telemetry unit 46 is also provided in the main module 40 toprovide information to the processor circuit 43 received from sourcesexternal to the body. Lastly, a timing circuit 42 is provided tocommunicate with an auxiliary module 50 through an optical communicationinterface 41 in the main module 40, over optical communication channels36, such as fiber optics, and through an optical communication interface46 in the auxiliary module 50. In response to the information receivedfrom the optical communication interface 46, a signaling logic circuit47 will activate or suppress a pacing unit 48. In this embodiment, ifthere is a failure in the main module 40 due to error or electromagneticinsult or interference, the signaling logic circuit 47 will detect theshutdown of the main module 40 and cause the auxiliary module 50 to takeover the pacing of the heart 49 in an asynchronous manner through pacingunit 48.

[0143] As described above, the cardiac assist system performssynchronous cardiac assist operations through a main module. A secondarymodule is provided to perform asynchronous cardiac assist operations.Upon detection of an electromagnetic interference insult upon thecardiac assist system, the control circuit of the main module terminatessynchronous cardiac assist operations, and the control circuit of thesecondary module initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult. The controlcircuit of the secondary module places the cardiac assist system in theasynchronous mode for a duration of the electromagnetic interferenceinsult and terminates the asynchronous mode of the cardiac assist systemupon detection of an absence of an electromagnetic interference insult.The control circuit of the main module terminates the synchronous modeof the cardiac assist system for the duration of the electromagneticinterference insult and re-initiates the synchronous mode of the cardiacassist system upon detection of an absence of an electromagneticinterference insult.

[0144]FIG. 4 is a more detail schematic of FIG. 3. In FIG. 4, a cardiacassist system is immune or hardened electromagnetic insult orinterference, namely to magnetic radiation imaging, MRI. As illustratedin FIG. 4, a main module 67 includes a parallel processing unit 59 andprimary and secondary processors 65 and 63 that control the operationsof the cardiac assist system. The parallel processing unit 59 providescontrol signals to a pacing unit 58. The pacing unit 58 produces packetsof energy to stimulate the heart to start beating or to beat at apredetermined rate or pace through lead(s) 51 and electrode 52. Theparallel processing unit 59 also receives information about theconditions of the heart 49 from a sensor 53 through lead(s) 56. Thesensor 53 monitors the conditions of the heart to provide feedbackinformation to the parallel processing unit 59.

[0145] A telemetry unit 62 is also provided in the main module 67 toprovide information to the parallel processing unit 59 received fromsources 60 external to the body. Memory 72 is provided for theprocessing of the cardiac assist system, and a primary error detectioncircuit 64 is included to detect any failures in the main module 67.Lastly, a timing circuit 66 is provided to communicate with an auxiliarymodule 69 through an optical emitter 68 in the main module 67, overoptical communication channels 70, such as fiber optics, and through alight detection and signaling circuit 73 in the auxiliary module 69.

[0146] In response to the information received from the light detectionand signaling circuit 73, a pacing unit 74 will activate or de-activate.In this embodiment, if there is a failure in the main module 67 due toerror or electromagnetic insult or interference, the light detection andsignaling circuit 73 will detect the shutdown of the main module 67 andcause the auxiliary module 69 to take over the pacing of the heart in anasynchronous manner through pacing unit 74, lead(s) 55, and electrode54.

[0147] As described above, the cardiac assist system performssynchronous cardiac assist operations through a main module. A secondarymodule is provided to perform asynchronous cardiac assist operations.Upon detection of an electromagnetic interference insult upon thecardiac assist system, the control circuit of the main module terminatessynchronous cardiac assist operations, and the control circuit of thesecondary module initiates asynchronous cardiac assist operations upondetection of the electromagnetic interference insult. The controlcircuit of the secondary module places the cardiac assist system in theasynchronous mode for a duration of the electromagnetic interferenceinsult and terminates the asynchronous mode of the cardiac assist systemupon detection of an absence of an electromagnetic interference insult.The control circuit of the main module terminates the synchronous modeof the cardiac assist system for the duration of the electromagneticinterference insult and re-initiates the synchronous mode of the cardiacassist system upon detection of an absence of an electromagneticinterference insult.

[0148]FIG. 30 illustrates a cardiac assist system that includes aprimary device housing 1100. The primary device housing 1100 includes acontrol circuit 1110, such as a microprocessor integrated circuit forcontrolling the operations of the cardiac assist system. The controlcircuit 1110 may select a mode of operation for the cardiac assistsystem based on predetermined sensed parameters. The primary devicehousing 1100 may also include circuitry (not shown) to detect andisolate cross talk between device pulsing operations and device sensingoperations. The control circuit 1110 may isolate physiological signalsusing a noise filtering circuit or a digital noise filtering.

[0149] The primary device housing 1100 is implantable such that thecontrol circuit 1110 can be programmable from a source external of theprimary device housing 1100 or the control circuit 1110 can providephysiological diagnostics to a source external of the primary devicehousing 1100.

[0150] The primary device housing 1100 includes a power source 1120. Thepower source 1120 may be a battery power source in combination with abattery power source measuring circuit. In this embodiment, the controlcircuit 1110 can automatically adjust a value for determining anelective replacement indication condition of a battery power source suchthat the value is automatically adjusted by the control circuit 1110 inresponse to a measured level of a state of the battery power source, themeasured level generated by the battery power source measuring circuitconnected to the battery power source.

[0151] The primary device housing 1100 includes an optical emitter 1130,an optical sensor 1140, and an interface 1170 to put the primary devicehousing 1100 in operative communication with a lead system 1150.

[0152] The primary device housing 1100 may also include a switch (notshown), such as a reed switch or solid state switch, to place thecontrol circuit 1110 into a fixed-rate mode of operation and an acousticsensor (not shown) or near infrared sensor (not shown) to sense apredetermined acoustic signal. The switch places the control circuit1110 into a fixed-rate mode of operation when the acoustic sensor ornear infrared sensor senses the predetermined acoustic signal or thepredetermined infrared signal.

[0153] The primary device housing 1100 has formed around it a shield1160 to shield the primary device housing 1100 and any circuits thereinfrom electromagnetic interference.

[0154] The shield 1160 may be a metallic sheath, a carbon compositesheath, or a polymer composite sheath to shield the primary devicehousing 1100 and any circuits therein from electromagnetic interference.The shield 1160 is further covered with a biocompatible material whereinthe biocompatible material may be a non-permeable diffusion resistantbiocompatible material. The primary device housing 1100 may also includea detection circuit (not shown) to detect a phase timing of an externalelectromagnetic field such that the control circuit 1110 alters itsoperations to avoid interfering with the detected externalelectromagnetic field.

[0155]FIG. 30 further illustrates a lead system 1150 connected to theprimary device housing 1100. The lead system 1150 provides acommunication path for information to be transported between the primarydevice housing 1100 and a distal location in the body. The lead system1150 also may be a conduit of power or energy from the primary devicehousing 1100 to the distal location in the body.

[0156] In the example illustrated in FIG. 30, the lead system 1150 mayprovide a path for control signals to be transferred to the distallocation of the body, such as the heart muscle tissue. These controlsignals are used to control the operations of a secondary device 1200,such as stimulating the beating of the heart. The lead system 1150 mayalso provide a path for signals representing sensed biologicalconditions to be transferred from the distal location of the body to theprimary device housing 1100 so that the functionality of the heartmuscle tissue can be effectively monitored.

[0157] The lead system 1150 may be a fiber optic based communicationsystem wherein the fiber optic communication system contains at leastone channel within a multi-fiber optic bundle. The fiber optic basedcommunication system is covered with a biocompatible material whereinthe biocompatible material is a non-permeable diffusion resistantbiocompatible material.

[0158] The lead system 1150 may also be a plurality of electrical leadsthat have a shield 1180 therearound to prevent the electrical leads fromconducting stray electromagnetic interference. This shield 1180 may be ametallic sheath, a carbon composite sheath, or a polymer compositesheath to prevent the electrical leads from conducting strayelectromagnetic interference. In addition to the shield 1180 or in lieuof the shield 1180, each electrical lead may include an electricalfilter wherein the electrical filter removes stray electromagneticinterference from a signal being received from the electrical lead. Theelectrical filter may comprise capacitive and inductive filter elementsadapted to filter out predetermined frequencies of electromagneticinterference. The shield 1180 is covered with a biocompatible materialwherein the biocompatible material is a non-permeable diffusionresistant biocompatible material.

[0159] The electrical leads maybe unipolar leads, bipolar leads, or acombination of unipolar and bipolar leads. The lead system 1150 may alsobe a combination of a fiber optic based communication system andelectrical leads.

[0160] The lead system 1150 may also include a detection circuit (notshown) to detect a phase timing of an external electromagnetic fieldsuch that the control circuit 1110 alters its operations to avoidinterfering with the detected external electromagnetic field.

[0161] In FIG. 30, the secondary housing 1200 includes a control circuit1210, such as a microprocessor integrated circuit. The secondary devicehousing 1200 may also include circuitry (not shown) to detect andisolate cross talk between device pulsing operations and device sensingoperations. The control circuit 1210 may isolate physiological signalsusing a noise filtering circuit or a digital noise filtering.

[0162] The secondary device housing 1200 includes a power source 1220.The power source 1220 may be a battery power source or capacitor orother device for storing. The primary device housing 1200 includes anoptical emitter 1230, an optical sensor 1240, and an interface 1270 toput the secondary device housing 1200 in operative communication withthe lead system 1150.

[0163] The secondary device housing 1200 has formed around it a shield1260 to shield the secondary device housing 1200 and any circuitstherein from electromagnetic interference.

[0164] The shield 1260 may be a metallic sheath, a carbon compositesheath, or a polymer composite sheath to shield the secondary devicehousing 1200 and any circuits therein from electromagnetic interference.The shield 1260 is further covered with a biocompatible material whereinthe biocompatible material may be a non-permeable diffusion resistantbiocompatible material.

[0165] The secondary housing 1200 may also include electrodes 1300 foreither stimulating a tissue region or sensing biological characteristicsor parameters from the tissue region. More details as to theconstruction of the secondary device are set forth below in thedescribing of distal end elements.

[0166] As an alternative to electrodes 1300, the secondary devicehousing 1200 may include a sensing and stimulation system that includesoptical pulsing components to deliver a stimulus of a predeterminedduration and power to the desired anatomical cardiac tissue region; asensing and stimulation system that includes optical pulsing componentsto deliver a stimulus of a predetermined duration and power to thedesired anatomical cardiac tissue region and electrical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region; a hydrostatic pressuresensing components to detect physiological signals from the desiredanatomical cardiac tissue region; or optical sensing components todetect physiological signals from the desired anatomical cardiac tissueregion and electrical sensing components to detect physiological signalsfrom the desired anatomical cardiac tissue region.

[0167] The secondary device housing 1200 may also include a detectioncircuit (not shown) to detect a phase timing of an externalelectromagnetic field such that the control circuit 1110 alters itsoperations to avoid interfering with the detected externalelectromagnetic field.

[0168] The secondary device housing 1200 may include sensors to detect aheart signal and to produce a sensor signal therefrom and a modulator tomodulate the sensor signal to differentiate the sensor signal fromelectromagnetic interference. In the alternative, the secondary devicehousing 1200 may include sensors to detect a heart signal and to producea sensor signal therefrom, and the primary device housing 1100 mayinclude a sampling circuit to sample the sensor signal multiple times todifferentiate the sensor signal from electromagnetic interference,undesirable acoustic signals, large muscle contractions, or extraneousinfrared light.

[0169] The cardiac assist system illustrated in FIG. 30 may detect anelectromagnetic interference insult upon the cardiac assist system, andupon detection, the control circuit 1110 places the cardiac assistsystem in an asynchronous mode. The control circuit 1110 places thecardiac assist system in the asynchronous mode for a duration of theelectromagnetic interference insult and places the cardiac assist systemin a synchronous mode upon detection of an absence of an electromagneticinterference insult. The electromagnetic interference insult may bedetected a thermistor or other heat detector, a high frequencyinterference detector, a high voltage detector, or an excess currentdetector.

[0170] The cardiac assist system illustrated in FIG. 30 may also provideatrial monitoring and diagnostic functions to help physicians make moreprecise patient management decisions. The cardiac assist systemillustrated in FIG. 30 can provide bradyarrhythmia therapies that treatpatients with chronic heart problems in which the heart beats too slowlyto adequately support the body's circulatory needs, in addition to themonitoring of the atria (upper chambers) and ventricles (lower chambers)to enable physicians to assess atrial rhythm control and ventricularrate control.

[0171] The cardiac assist system illustrated in FIG. 30 can also be usedto provide daily atrial fibrillation measurements to assess atrialrhythm control. This information can improve a physician's ability totrack disease progression, as well as the effectiveness of currentdevice and drug therapies. The cardiac assist system illustrated in FIG.30 can also be used to monitor of the ventricular rate during an atrialarrhythmia that helps assess ventricular rate control. This informationcan be viewed in a graphical snapshot format or by viewing the specificepisode EGM information. The cardiac assist system illustrated in FIG.30 can also be used to provide specific information on the frequency andduration of arrhythmias that help with risk assessment of symptoms andin determining whether a change in anticoagulation medicines iswarranted.

[0172]FIG. 27 illustrates an MRI-compatible cardiac pacemaker accordingto another embodiment of the present invention. The pacemaker may bewearable and is readily implemented to operate in a fixed-rate (VOO)mode. The pacemaker includes a first (main) enclosure 263 that isdesigned to be located outside the body and connected to a proximal end268 of a photonic catheter. A distal end 273 of a photonic catheter 271mounts a bipolar endocardial (or pericardial) electrode pair 286 thatincludes a second enclosure 283 and a third enclosure 285 separated by ashort insulative spacer 284. Other electrode configurations could alsobe used.

[0173] The main enclosure 263 houses a self-contained electrical powersource 264, a pulse generator 265, and an electro-optical transducer266. The power source 264, which may include one or more batteries,serves to deliver low energy continuous electrical power to the pulsegenerator. The pulse generator 265 stores the electrical energy providedby the power source 264 in one or more storage devices such ascapacitors, batteries, etc., and periodically releases that energy todeliver electrical pulses to the electro-optical transducer 266. Theelectro-optical transducer 266 converts the electrical pulses into lightenergy and directs that energy into the proximal end 268 of the photoniccatheter 271.

[0174] The main enclosure 263 is preferably formed as a sealed casing,external to the body, made from a non-magnetic metal. Note that a ratecontrol selector and a pulse duration selector can be provided on themain enclosure 263 to allow a medical practitioner to controllablystress a patient's heart by varying the rate and duration of thestimulating pulses. Note further that if the power source 264 comprisesmultiple batteries, these may be separately wired for independentoperation and a selector switch can be provided on the enclosure 263 toselectively activate each battery for use. A pair of illuminated pushbuttons may also be provided for testing each battery.

[0175] The photonic catheter 271 includes an optical conduction pathway267 surrounded by a protective outer covering 269. The opticalconduction pathway 267 may be constructed with one or more fiber optictransmission elements that are conventionally made from glass or plasticfiber material, e.g., a fiber optic bundle. To avoid body fluidincompatibility problems, the protective outer covering 269 should bemade from a biocompatible material, such as silicone rubber,polyurethane, polyethylene, or other biocompatible polymer having therequired mechanical and physiological properties. The protective outercovering 269 is thus a biocompatible covering. Insofar as the photoniccatheter 271 must be adapted for insertion into the body, thebiocompatible covering 269 is preferably a very thin-walled elongatedsleeve or jacket having an outside diameter on the order of about 5millimeters and preferably as small as one millimeter or even smaller.This will render the photonic catheter 271 sufficiently slender tofacilitate insertion thereof through a large vein, such as the externaljugular vein.

[0176] The proximal end 268 of the photonic catheter 271 is mounted tothe main enclosure 263 using an appropriate connection. The opticalconduction pathway 267 may extend into the enclosure 263 for a shortdistance, where it terminates in adjacent relationship with theelectro-optical transducer 266 in order to receive light energytherefrom.

[0177] Light emitted by the electro-optical transducer 266 is directedinto the proximal end 268 of the photonic catheter 271, and transmittedthrough the optical conduction pathway 267 to the second enclosure 283.Since the photonic catheter 271 is designed for optical transmission, itcannot develop magnetically induced or RF-induced electrical currents,as is the case with the metallic leads of conventional pacemakercatheters.

[0178] The second enclosure 283 houses an opto-electrical transducer274, which converts light energy received from the distal end of thephotonic catheter 271 into electrical energy. The electrical output side280 of the opto-electrical transducer 274 delivers electrical pulsesthat drive the pacemaker's electrode pair 286.

[0179] The second enclosure 283 is a hermetically sealed casing madefrom a non-magnetic metal, such as titanium, a titanium-containingalloy, platinum, a platinum-containing alloy, or any other suitablemetal, including copper plated with a protective and compatible coatingof the foregoing materials. Plated copper is especially suitable for thesecond enclosure 283 because it has a magnetic susceptibilityapproaching that of the human body, and will therefore minimize MRIimage degradation. Note that the magnetic susceptibility of human bodytissue is very low, and is sometimes diamagnetic and sometimesparamagnetic. As an alternative to using non-magnetic metals, the secondenclosure 283 can be formed from an electrically conductive non-metalthat preferably also has a very low magnetic susceptibility akin to thatof the human body. Non-metals that best approach this condition includeconductive composite carbon and conductive polymers comprising silicone,polyethylene, or polyurethane.

[0180] Unlike the main enclosure 263, the second enclosure 283 isadapted to be implanted via insertion in close proximity to the heart,and in electrical contact therewith. As such, the second enclosure 283preferably has a miniaturized tubular profile that is substantiallyco-equal in diameter with the photonic catheter 271.

[0181] As seen In FIGS. 27 and 28, the second enclosure (283, 295)includes a cylindrical outer wall 276 and a pair of disk-shaped endwalls 272 and 277. The end wall 272 is mounted to the distal end 273 ofthe photonic catheter 271 using an appropriate sealed connection thatprevents patient body fluids from contacting the optical conductionpathway 267 and from entering the second enclosure (283, 295). Althoughthe photonic catheter 271 may feed directly from the main enclosure 263to the second enclosure (283, 295), another arrangement would be toprovide an optical coupling 270 at an intermediate location on thephotonic catheter 271. The coupling 270 could be located so that adistal portion of the photonic catheter 271 that connects to the secondenclosure 283 protrudes a few inches outside the patient's body. Aproximal portion of the photonic catheter 271 that connects to the mainenclosure 263 would then be connected when MRI scanning is to beperformed. Note that the main enclosure 263 could thus be located aconsiderable distance from the patient so as to be well outside the areaof the MRI equipment, as opposed to being mounted on the patient or thepatient's clothing.

[0182] In an alternative arrangement, the coupling 270 could be locatedat the main enclosure 263. The optical conduction pathway 267 may extendinto the enclosure (283, 295) for a short distance, where it terminatesin adjacent relationship with the opto-electrical transducer (274, 289)in order to deliver light energy thereto. Light received by theopto-electrical transducer (274, 289) will thus be converted toelectrical energy and delivered to the output side 280 of theopto-electrical transducer (274, 289).

[0183] Due to the miniature size of the second enclosure (283, 295), theoptoelectrical transducer (274, 289) needs to be implemented as aminiaturized circuit. However, such components are conventionallyavailable from commercial electronic component manufacturers. Note thatthe opto-electrical transducer (274, 289) also needs to be adequatelysupported within the second enclosure (283, 295).

[0184] To that end, the second enclosure (283, 295) can be filled with asupport matrix material 291 that may be the same material used to formthe photonic catheter's biocompatible covering 269 (e.g., siliconerubber, polyurethane, polyethylene, or any biocompatible polymer withthe required mechanical and physiological properties).

[0185] As stated above, the second enclosure (283, 295) represents partof an electrode pair (286, 298) that delivers the electrical output ofthe pacemaker to a patient's heart. In particular, the electrode pair(286, 298) is a tip/ring system and the second enclosure (283, 295) isused as an endocardial (or pericardial) ring electrode thereof. Apositive output lead (275, 290) extending from the electrical outputside 280 of the opto-electrical transducer (274, 289) is electricallyconnected to the cylindrical wall 276 of the second enclosure (283,295), as by soldering, welding or the like. A negative output lead (281,294) extending from the electrical output side 280 of theopto-electrical transducer (274, 289) is fed out of the second enclosure(283, 295) and connected to a third enclosure (285, 297), whichfunctions as an endocardial tip electrode of the electrode pair (286,298).

[0186] The third enclosure (285, 297) can be constructed from the samenonmagnetic metallic material, or non-metal material, used to form thesecond enclosure (283, 295). Since it is adapted to be inserted in apatient's heart as an endocardial tip electrode, the third enclosure(285, 297) has a generally bullet shaped tip (279, 293) extending from atubular base end (278, 292). The base end (278, 292) preferably has anoutside diameter that substantially matches the diameter of the secondenclosure (283, 295) and the photonic catheter 271. Note that the baseend (278, 292) of the third enclosure (285, 297) is open insofar as thethird enclosure (285, 297) does not house any critical electricalcomponents. Indeed, it mounts only the negative lead (281, 294) that iselectrically connected to the third enclosure's base end (278, 292), asby soldering, welding, or the like.

[0187] The material used to form the spacer (284, 296) preferably fillsthe interior of the second enclosure (283, 295) so that there are novoids and so that the negative lead (281, 294) is fully capturedtherein.

[0188] In FIG. 29, electrical power source 303 is implemented using apair of conventional pacemaker lithium batteries 300 providing a steadystate DC output of about 3 to 9 volts. Electro-optical transducer 301 isimplemented with light emitting or laser diodes 304 and current limitingresistors 305. The diodes 304 are conventional in nature and thus have aforward voltage drop of about 2 volts and a maximum allowable currentrating of about 50-100 milliamperes, or more. If additional supplyvoltage is available from the power source 20 (e.g., 4 volts or higher),more than one diode can be used in the electro-optical transducer foradditional light energy output. The value of each resistor 305 isselected accordingly.

[0189] By way of example, if the batteries 300 produce 3 volts and thedesired current through a single diode is 0.5 milliamperes, the value ofthe resistor should be about 2000 ohms. This would be suitable if thediode is a light emitting diode. If the diode were a laser diode, othervalues and components would be used. For example, a current level on theorder of 100 milliamps may be required to produce coherent light outputfrom the diode if it is a laser. The optical conduction pathway 300 canbe implemented as fiber optic bundles 307, or as single fibers, drivingrespective arrays of photo diodes. The opto-electrical transducer 28 maybe implemented with six photodiodes 312-317 that are wired forphotovoltaic operation.

[0190] The opto-electrical transducer 309 may be implemented with asingle photodiode that is wired for photovoltaic operation. Thephotodiodes are suitably arranged so that each respectively receives thelight output of one or more fibers of the fiber optic bundles and isforward biased into electrical conduction thereby.

[0191] Each photodiode is conventional in nature and thus produces avoltage drop of about 0.6 volts. Cumulatively, the photodiodes develop avoltage drop of about 3.3 volts across the respective positive andnegative inputs a power amplifier (not shown). The photodiode developsabout 0.6 volts across the respective positive and negative inputs ofthe power amplifier.

[0192] FIGS. 40-42 and 49 shows an alternative circuit configurationthat may be used to implement the oscillator (369, 372, 373, 439) andthe power amplifier. The alternative circuit configurations areconventional in nature and do not constitute part of the presentinvention per se. The alternative circuit configurations are presentedherein as examples of pulsing circuits that have been shown to functionwell in a pacemaker environment. In FIGS. 40-42, the oscillator (369,372, 373, 439) is a semiconductor pulsing circuit (365, 370, 374, 441)of the type disclosed in U.S. Pat. No. 3,508,167. As described in U.S.Pat. No. 3,508,167, the contents of which are incorporated herein byreference, the pulsing circuit (365, 370, 374, 441) forming theoscillator (369, 372, 373, 439) provides a pulsewidth and pulse periodthat are relatively independent of load and supply voltage. Thesemiconductor elements are relegated to switching functions so thattiming is substantially independent of transistor gain characteristics.In particular, a shunt circuit including a pair of diodes is connectedso that timing capacitor charge and discharge currents flow throughcircuits that do not include the base-emitter junction of a timingtransistor.

[0193] In FIG. 46, an opto-electrical coupling device 399 is shown. Theopto-electrical coupling device includes opto-electrical transducer 392.A high quality capacitor 390 delivers pulses from the opto-electricaltransducers photodiode array (393-398) to a tip electrode 401. A returnpath is provided from a ring electrode 400. The capacitor 390 forms partof a DC current discharge system 391 that also includes a resistor 389.The resistor 389 is connected across the capacitor 390 to discharge itbetween pulses. Exemplary values for the capacitor 390 and the resistor389 are 10 microfarads and 20K ohms, respectively.

[0194] In FIG. 47, a constant current regulator 402 is shown. Thepurpose of the constant current regulator 402 is to controllably drivethe electro-optical transducer 405 using the electrical pulse output ofa pulse generator. Collectively, the constant current regulator 402 andthe electro-optical transducer 405 provide a constant current regulatedlaser light generator 404. The current regulator 402 uses an NPNtransistor 403 arranged in a common emitter configuration to drive thelaser diode 404. A suitable NPN transistor that may be used to implementthe transistor 403 is a switching transistor.

[0195] The laser diode 404 can be implemented as a standard 150milliwatt gallium arsenide laser diode. The recommended power level fordriving such a device is about 100 milliwatts. The required inputvoltage is about 2 volts. Assuming there is a conventional diode voltagedrop of about 0.7 volts across the laser diode 404, a driving current ofabout 140 milliamps should be sufficient to achieve operation at thedesired 100 milliwatt level. However, the current through the laserdiode 404 must be relatively constant to maintain the desired poweroutput. The constant current regulator 402 achieves this goal.

[0196] In particular, the base side of the transistor 403 is biasedthrough a resister R1 and a pair of diodes D1 and D2. The diodes D1 andD2 are connected between the base of the transistor 403 and ground. Eachhas a conventional diode voltage drop of about 0.7 volts, such that thetotal voltage drop across the diodes D1 and D2 is about 1.5 volts and issubstantially independent of the current through the diodes (atoperational current levels). This means that the base of the transistor403 will be maintained at a relatively constant level of about 1.5 voltsnotwithstanding changes in the input voltage supplied from the pulsegenerator. The value of the resistor R1 is selected to be relativelyhigh to reduce the current draw through the base of the transistor 403.By way of example, a value of 2500 ohms may be used for R1. Assuming asupply voltage of about 5 volts, as represented by the input pulsewaveform, the current through the resistor R1 will be a negligible 1.4milliamps.

[0197] Importantly, the emitter side of the transistor 403 will remainat a relatively constant level of about 1 volt (assuming a base-emittervoltage drop across the transistor 403 of about 0.5 volts). A resistorR2 is placed between the emitter of the transistor 403 and ground inorder to establish a desired current level through the collector-emittercircuit of the transistor 403. Note that this also represents thedriving current through the laser diode 404 insofar as the laser diodeis connected in series between the current regulator's supply voltage(the output of pulse generator) and the collector of the transistor 406.Since the voltage potential at the transistor emitter is about 1 volt,if R2 is selected to be a 7 ohm resistor, the resultant current levelwill be about 140 milliamps. This corresponds to the current levelrequired to drive the laser diode 404 at the desired operational powerlevel.

[0198] In FIG. 48, an electrical power source (409, 411) is implementedusing a pair of conventional pacemaker lithium batteries (408, 410)providing a steady state DC output of about 3 to 9 volts. Theelectro-optical transducers 412 and 416 are implemented with lightemitting or laser diodes (414, 415) and current limiting resistors (413,419). The diodes are conventional in nature and thus have a forwardvoltage drop of about 2 volts and a maximum allowable current rating ofabout 50-100 milliamps, or more. If additional supply voltage isavailable from the power source (409, 411) (e.g., 4 volts or higher),more than one diode can be used in each electro-optical transducer 412and 416 for additional light energy output. The value of each resistoris selected accordingly.

[0199] By way of example, if the batteries produce 3 volts and thedesired current through a single diode is 0.5 milliamps, the value ofthe resistor should be about 2000 ohms. This would be suitable if thediode is a light emitting diode. If the diode were a laser diode, othervalues and components would be used. For example, a current level on theorder of 100 milliamps may be required to produce coherent light outputfrom the diode if it is a laser. The optical conduction pathways 417 and421 can be implemented as fiber optic bundles 418 and 423, or as singlefibers, driving respective arrays of photodiodes.

[0200] The opto-electrical transducer 424 may be implemented with sixphotodiodes 428-433 that are wired for photovoltaic operation. Theopto-electrical transducer 424 may be implemented with a singlephotodiode 434 that is wired for photovoltaic operation. The photodiodesare suitably arranged so that each respectively receives the lightoutput of one or more fibers of the fiber optic bundles 418 and 423 andis forward biased into electrical conduction thereby.

[0201] Each photodiode is conventional in nature and thus produces avoltage drop of about 0.6 volts. Cumulatively, the photodiodes 428-433develop a voltage drop of about 3.3 volts across the respective positiveand negative inputs 426 and 435 of the power amplifier 427. Thephotodiode 434 develops about 0.6 volts across the respective positiveand negative inputs 437 and 438 of the power amplifier 427.

[0202] In FIG. 43, a circuit diagram of an opto-electric coupling device388 is shown. The opto-electric coupling device 388 includes theopto-electrical transducer 376, which is assumed to be illuminated by aphotonic catheter for about 1 millisecond, and left dark for about 1000milliseconds. When illuminated, opto-electrical transducer photodiodearray 377-382 will produce pulses of about 3 to 4 volts across itsoutputs. The positive side of the photodiode array is connected via ahigh quality capacitor 385 to an implantable tip electrode 383 that isadapted to be implanted in the endocardium of a patient. The negativeside of the photodiode array is connected to an implantable ringelectrode 384 that is adapted to be immersed in the blood of thepatient's right ventricle. A DC current discharge system 387 comprisingthe capacitor 385 and a resistor 386 is used to attenuate DC current inthe tissue implanted with the electrodes 383 and 384.

[0203] The resistor 386 is connected across the outputs of thephotodiode array. The resistor 386 thus grounds one side of thecapacitor 385 between pulses. The return path from the implanted tissueis the through the ring electrode 384.

[0204] The values of the capacitor and the resistor are selected so thatthe opto-electric coupling device conveys a suitable stimulating signalto the electrodes, but in such a manner as to prevent any net DC currentfrom flowing into the implanted tissue. A long RC time constant isdesired so that the square waveform of the photodiode array output isdelivered in substantially the same form to the implanted tissue. For a1 millisecond pulse, the desired RC time constant should besubstantially larger than 1 millisecond. By way of example, if thecapacitor has a capacitance of 10 microfarads and the resistor has aresistance of 20K ohms, the RC time constant will be 200 milliseconds.This is substantially larger than the 1 millisecond pulse lengthproduced by the photodiode array.

[0205] On the other hand, the RC time constant should not be so large asto prevent adequate DC current flow from the implanted body tissue intothe capacitor between pulses. According to design convention for RCcircuits, a period of five time constants is required in order for an RCcircuit capacitor to become fully charged. Note that the selected RCtime constant of 200 milliseconds satisfies this requirement if thephotodiode array is pulsed at 1000 millisecond intervals, which istypical for pacemakers. Thus, there will be approximately five 200millisecond time constants between every pulse. Stated another way, theRC time constant will be approximately one-fifth of the time intervalbetween successive pulses.

[0206]FIG. 44 shows the square wave electrical pulses generated by thephotodiode array. FIG. 45 shows the actual electrical pulses deliveredat the electrodes due to the presence of the RC circuit provided by thecapacitor and the resistor. Note that the pulses of FIG. 45 aresubstantially square is shape due to the RC circuit's time constantbeing substantially larger than the input pulse width. FIG. 45 furthershows that there is a small reverse potential between pulses thatcounteracts DC current build up in the stimulated tissue.

[0207] Ideally, the area A₁ underneath each positive pulse of FIG. 45will be equal to the area A₂ of negative potential that follows thepositive pulse.

[0208] Another embodiment of the present invention is the use of aphotonic catheter in a MRI environment to sense the biologicalconditions of particular tissue regions of a patient or to stimulateparticular tissue regions of the patient. Examples of photonic cathetersare illustrated in FIGS. 5 through 20.

[0209] In FIGS. 5 and 6, power supply 595 and logic and control unit 597enable emitter 598 to transmit radiation, preferably optical radiationat wavelength λ₁ through beam splitter 900 into wave-guide 601. Thisradiation exits the wave-guide 601 and passes through beam splitter 606to sensor 607 that converts the radiation to electrical energy. Theelectrical energy is used to directly power functions at the distal endof lead 602, such as stimulation of internal body tissues and organs(e.g. pacing of cardiac tissues) through electrodes 604 and 603. Theelectrical energy is also used to power logic and control unit 608 or isstored in energy storage device 609 (e.g. a capacitor) for later use.Proximally located elements are electrically connected throughconductors. Distally located sensor 607, logic and control unit 608,energy storage device 609, and electrodes (604, 603) are electricallyconnected through conductive elements.

[0210] A second emitter 600 transmits radiation at wavelength λ₂ (λ₂≠λ₁)through beam splitter 901, off beam splitter 900, into wave-guide 601,to beam splitter 606 and optical attenuator 605 that is mounted on amirror. The optical attenuator 605 is preferably made from materialssuch as liquid crystals whose optical transmission density is modulatedby applied electrical voltage. The distally located logic and controlunit 608 and optical attenuator 605 are powered either directly byexcitation radiation or from energy stored in energy storage element609.

[0211] This photonic catheter can also be used with electrodes 603 and604 to capture electrical signals from the patient and direct thecaptured electrical signals to logical and control unit 608 which useselectrical energy to modulate the optical transmission density ofoptical attenuator 605. Attenuated optical signals, originally emanatingfrom emitter 600, are encoded with the electrical signals received byelectrodes 603 and 604 by passing through the optical attenuator 605,reflect off mirror, travel back through the optical attenuator 605,reflect off beam splitter 606 and into wave-guide 601 to beam splitters900 and 901 to sensor 599 that converts the encoded optical signal to anencoded electrical signal. Output from sensor 599 is sent to logic andcontrol unit 597. This output is either utilized by logic and controlunit 597 to control the radiation from emitter 598, which is typicallyat a high energy level and is used to stimulate distally located tissuesand organs, or is relayed to transmitter 596 which relays this sensoryinformation to external sources.

[0212] The embodiment illustrated in FIG. 7 is similar to the embodimentillustrated in FIGS. 5 and 6, with the exception that the opticalattenuator 612 is mounted over the surface of the distally locatedsensor 613 to take advantage of the first surface reflectance of thissensor. Radiation emitted by wave-guide 610 passes through opticalattenuator 612 to sensor 613 that converts the radiation to electricalenergy as previously described. Radiation emitted by wave-guide 610passes through optical attenuator 612 and reflects off the front surfaceof sensor 613. This reflected energy is collected by coupling lens 611that directs the energy into wave-guide 610 to a sensor at the proximalend (not shown).

[0213] The embodiment illustrated in FIG. 8 is similar to the embodimentillustrated in FIGS. 5 and 6, with the exception that a variablereflectance optical reflector 616 is mounted over the surface of thedistally located sensor 617. Radiation emitted by wave-guide 619 passesthrough optical reflector 616 to sensor 617 that converts the radiationto electrical energy as previously described. Radiation emitted bywave-guide 619 is reflected off optical reflector 616 and is collectedby coupling lens 618 that directs the energy into wave-guide 619.Preferably, the variable reflectance optical reflector 616 would betransparent to excitation radiation.

[0214] With respect to FIGS. 9 and 10, power supply 620 and logic andcontrol unit 622 enable emitter 623 to transmit radiation, preferablyoptical radiation at wavelength λ₁ through beam splitter 624 intowave-guide 626. This radiation exits the wave-guide and passes throughan on-axis variable intensity optical emitter 631 to sensor 632 thatconverts the radiation to electrical energy. The electrical energy isused to directly power functions at the distal end of lead 635, such asstimulation of internal body tissues and organs (e.g. pacing of cardiactissues) through electrodes 627 and 628; to power logic and control unit633; or to store in energy storage device 634 (e.g. a capacitor) forlater use. Proximally located elements are electrically connectedthrough conductors. Distally located sensor, logic and control unit,energy storage device, and electrodes are electrically connected throughconductive elements.

[0215] Logic and control unit 633 receives sensor input from electrodes627 and 628 and delivers an electrical potential to variable intensityoptical emitter 631 causing it to emit optical radiation at wavelengthλ₂ (λ₂≠λ₁) which is collected by coupling lens 630 and directed intowave-guide 629, to beam splitter 624 and sensor 625. The distallylocated logic and control unit 633 and optical attenuator 631 arepowered either directly by excitation radiation or from energy stored inenergy storage element 634.

[0216] This photonic catheter can also be used with electrodes 627 and628 to capture electrical signals from the patient and direct thecaptured electrical signals to logical and control unit 633 that useselectrical energy to modulate the variable intensity optical emitter631. Optical signals, emanating from variable intensity optical emitter631, are encoded with the electrical signals received by electrodes 627and 628 and travel into wave-guide 629 to beam splitter 624 to sensor625 that converts the encoded optical signal to an encoded electricalsignal. Output from sensor 625 is sent to logic and control unit 622.This output is either utilized by logic and control unit 622 to controlthe radiation from emitter 623, which is typically at a high energylevel and is used to stimulate distally located tissues and organs, oris relayed to transmitter 621 which relays this sensory information toexternal sources.

[0217] The embodiment illustrated in FIGS. 11 and 12 is similar to theembodiment illustrated in FIGS. 9 and 10, with the exception that thevariable intensity optical emitter 646 is located off-axis. Power supply636 and logic and control unit 638 enable emitter 639 to transmitradiation, preferably optical radiation at wavelength λ₁ through beamsplitter 910 into wave-guide 641. This radiation exits the wave-guide643 and passes through beam splitter 645 to sensor 647 that converts theradiation to electrical energy. The electrical energy is used todirectly power functions at the distal end of lead 642, such asstimulation of internal body tissues and organs (e.g. pacing of cardiactissues) through electrodes 650 and 644; power logic and control unit648; or to be stored in energy storage device 649 (e.g. a capacitor) forlater use.

[0218] Proximally located elements are electrically connected throughconductors. Distally located sensor 647, logic and control unit 648,energy storage device 649, and electrodes 650 and 644 are electricallyconnected through conductive elements. Variable intensity emitter 646transmits radiation at wavelength λ₂ (λ₂≠λ₁) off beam splitter 645 intowave-guide 643 and off beam splitter 910 to sensor 640. Preferably, thevariable intensity emitter 646 emits optical radiation when excited byan electrical potential, and is mounted upon a mirror to direct agreater percentage of emissions into wave-guide 643.

[0219] A preferred application of the embodiment illustrated in FIGS. 11and 12 uses electrodes 650 and 644 to capture electrical signals anddirect them to logical and control unit 648 which delivers electricalenergy to emitter 646 to emit optical radiation that is encoded with theelectrical signals received by electrodes 650 and 644. The encodedoptical signals are directed to beam splitter 645 and into wave-guide643 to sensor 640 that converts the encoded optical signal to an encodedelectrical signal. Output from sensor 640 is sent to logic and controlunit 638. This output is either utilized by logic and control unit 638to control the radiation from emitter 639, which is typically at a highenergy level (typically higher than radiation from emitter 646) and isused to stimulate distally located tissues and organs, or is relayed totransmitter 637 that relays this sensory information to externalsources.

[0220] In FIGS. 13 and 14, radiation emitter 651 transmits radiation,preferably optical radiation at wavelength λ₁ through beam splitter 652into wave-guide 655. This radiation exits wave-guide 656 at exit angle αand impinges upon sensor 657 that converts the radiation to electricalenergy. The electrical energy is used as previously described.Proximally and distally located elements are electrically connectedthrough conductors.

[0221] A second emitter 658 located on or within sensor 657 transmitsradiation at wavelength λ₂ (λ₂≠λ₁) at cone angle into wave-guide 656 tobeam splitter 652. The small size ‘d’ of emitter 658 relative to thelarger size ‘D’ of sensor 658 and narrow radiation exit angle a andemission angle β enable effective coupling of radiation from emitter 651into sensor 657 and radiation from emitter 658 into wave-guide 656.Optional coupling lens 653 collects and directs radiation to sensor 654.The distally located light source may be a solid-state laser or lightemitting diode.

[0222] In FIGS. 15 and 16, radiation emitter 659 transmits radiation,preferably optical radiation at wavelength λ₁ and exit angle β₁ throughoptional coupling lens 661 into wave-guide 662. This radiation exitswave-guide 663 at exit angle oil and impinges upon sensor 664 thatconverts the radiation into electrical energy. The electrical energy isused as previously described.

[0223] A second emitter 665 located on or within sensor 664 transmitsradiation at wavelength λ₂ at cone angle β₂ into wave-guide 663. Thisradiation exits wave-guide 662 at exit angle α₂ onto sensor 660.Ideally, wavelength λ₂≠λ₁ so that optical reflections from coupling lens661 or wave-guide 662 do not interfere with radiation incident upondetector 660. The small sizes ‘d’ of emitters 659 and 665 relative tothe larger sizes ‘D’ of sensors 660 and 664, combined with narrowradiation exit angles α₁ and α₂, and β₁ and β₂, enable effectivecoupling of radiation into wave-guide (662, 663), and sensors 660 and664.

[0224] In FIGS. 17 and 18, radiation emitter 666 transmits radiation,preferably optical radiation at wavelength λ₁ into wave-guide 667. Thisradiation exits wave-guide 670 and impinges upon sensor 671 thatconverts the radiation into electrical energy. The electrical energy isused as previously described.

[0225] A second distally located emitter 672 transmits radiation atwavelength λ₂ into wave-guide 673. This radiation exits wave-guide 668onto proximally located sensor 669. Wavelength λ₂ may or may not beequal to wavelength λ₁. Light sources 666 and 672 include a solid-statelaser or light emitting diode. Wave-guides (667, 670) and (668, 673) arepreferably included in the same lead assembly.

[0226] In FIGS. 19 and 20, a sensor 678 transparent to certainwavelengths of optical radiation is used. Radiation emitter 677transmits radiation, preferably optical radiation at wavelength λ₁through sensor 678 that is transparent to wavelength λ₁ into wave-guide679 and exiting at exit angle α to sensor 682 that converts theradiation to electrical energy. The electrical energy is used aspreviously described.

[0227] A second emitter 681 located on or within sensor 682 transmitsradiation at wavelength λ₂ (λ₂≠λ₁) at cone angle β into wave-guide 680to proximally located sensor 678 where it is absorbed and converted intoelectrical energy. As before, the small size ‘d’ of emitter 681 relativeto the larger size ‘D’ of sensor 682 and narrow radiation exit angle αand emission angle β enable effective coupling of radiation from emitter677 into sensor 682 and radiation from emitter 681 into wave-guide 680.

[0228]FIG. 50 illustrates another embodiment of the present invention inwhich a hermetic housing is constructed to provide part of an electrodetermination pair 448. The electrode termination pair 448 includes acup-shaped structure (tip) 449 acting as a tip electrode and thehermetic housing 446 (ring) acting as a ring electrode. The tip 449 andthe ring 446 are both substantially cylindrical in shape, and preferablyhave the same wall thickness. Note that the tip 449 has a rounded noseportion and a base portion that is planar in cross-section. The ring 446has proximal and distal end portions that are both preferably planar incross section.

[0229] As shown in FIG. 51, the tip 473 and the ring 463 can be madefrom a body-compatible, non-ferromagnetic metal such platinum, titaniumor alloy of platinum or titanium. As shown FIGS. 52 and 53, the tip(497, 522) and the ring (487, 515) can be made of a non-metallicmaterial, such as ceramic, and covered with electrically conductivecoatings (495, 520) and (480, 505), respectively. The difference betweenFIGS. 52 and 53 is that all exposed surfaces of the tip 497 and the ring487 are coated in FIG. 52, whereas only the outer surface of the tip 522and the ring 515 are coated in FIG. 53.

[0230] If a ceramic is used to form the tip and the ring, the materialused is preferably a suitable biocompatible ceramic material such aceramic of the type commonly used for joint prostheses. By way ofexample only, such material is available from Ceramic Components Inc. ofLatrobe, Pa. To form a ceramic tip and ring, ceramic slurry can beformed into the desired shapes and fired to bake the ceramic material.

[0231] The electrically conductive coatings (495, 520) and (480, 505)are preferably formed by very thinly coating the tip and the ring, as byelectroplating, sputtering or other deposition technique, etc., with asuitable metal. To facilitate MRI compatibility, the metal preferablyhas low magnetic susceptibility, such as titanium, platinum, an alloy oftitanium or platinum, or the like. Preferably, the coatings (495, 520)and (480, 505) are applied as thin as possible to achieve the twin goalsof efficient electrical interaction with implanted tissue whileminimizing interaction with MRI induced electromagnetic fields. By wayof example, the thickness of the coatings (495, 520) and (480, 505) mayrange from mono-molecular thickness to sub-micron or micron levelthickness.

[0232]FIGS. 50 through 53 show the electrode termination pair (448, 469,498, 524) being mounted to the distal end of a photonic catheter (451,476, 501). The tip and the ring are also interconnected by a shortinsulative stub (447, 468, 493, 518) that is solid, generallycylindrical in shape, and made from silicone, polyurethane,polyethylene, or any other suitable biocompatible electricallyinsulating material. The outside diameter of the stub preferably equalsthe outside diameter of the tip and the ring, to facilitate efficientimplantation and removal in a patient. The ends of the stub can bebonded to the tip and the ring using a suitable medical adhesive. Toprovide additional connection integrity, the stub can be formed with endportions (470, 492, 519) of reduced diameter. One end portion of thestub is received into an opening (471, 494) in the base portion of thetip and bonded therein. The other end portion of the stub is receivedinto an opening (459, 485, 509) in the distal end of the ring and bondedtherein.

[0233] The completed tip/ring assembly can be mounted to the distal endof the photonic catheter in similar fashion. In particular, the photoniccatheter will be a generally cylindrical element whose exterior sheath(451, 474, 459) is made from silicone, polyurethane, polyethylene, orany other suitable biocompatible electrically insulating material. Notethat the sheath could be tubular in shape, with a small center borecarrying one or more optical conductors therein. Alternatively, thesheath could be formed around the optical conductors such that theconductors are embedded, in the material of the sheath

[0234] In either case, the outside diameter of the sheath willpreferably be the same as that of the ring and can be bonded theretousing a suitable medical adhesive. To provide additional connectionintegrity, the sheath may be formed with a small end portion (453, 477,502) of reduced diameter that is snugly received within an opening (454,478, 503) in the proximal end the ring and bonded therein.

[0235] Since the ring functions as a hermetically sealed componenthousing, it must be provided with hermetically sealed closures at ornear the ends thereof. These closures may be provided by a pair ofclosure walls (465, 488, 516) and (461, 482, 513) that are securedwithin the interior of the ring. The closure walls can be formed fromany suitable bio-compatible material capable of sealing the ringinterior, including metals, polymers, and potentially other materials.To facilitate the secure hermetic attachment of the closure walls, theinside of the ring can be formed with a pair of recessed annularshoulders (456, 479, 504).

[0236] There may be disposed within the ring any number of componentsfor delivering electrical signals to, or sensing biological activity in,a body. Such components are collectively shown as a component array byreference numeral (462, 486, 514), and may include opto-electricaltransducers, electro-optical transducers, signal processors andamplifiers, digital microprocessors, temperature sensors, R-wavesensors, partial oxygen sensors, and any number of other components. Toprovide electrical interaction with surrounding body tissue, a positiveterminal of the component array is connected to a short metallic lead(457, 483, 507) made from copper or other suitable material of lowmagnetic susceptance.

[0237] In FIG. 51, the lead 457 is electrically connected to the ring byattaching it, as by soldering or the like, directly to the ring itself.In FIG. 52, the metallic lead 483 is electrically connected to the ringby attaching it, as by soldering or the like, to an interior portion ofthe metallic coating 480. In FIG. 53, the metallic lead 507 is fedthrough a small hole 506 in the wall of the ring so that it may beattached to the exterior metallic coating 505, as by soldering or thelike.

[0238] A negative terminal of the component array connects to a longermetallic lead (466, 489, 517) that is also made from copper or othersuitable material of low magnetic susceptance. This metallic lead feedsthrough a hermetic seal terminal (464, 490, 511) mounted on the closurewall. This metallic lead then extends through the material of the stub(which can be molded around the lead) and into the tip.

[0239] In FIG. 51, the metallic lead is electrically attached, as bysoldering or the like, directly to the tip itself. In FIG. 52, themetallic lead is electrically attached, as by soldering or the like, toan interior portion of the metallic coating. In FIG. 53, the metalliclead is fed through a small hole 523 in the ceramic wall of the tip sothat it may be attached to the metallic coating, as by soldering or thelike.

[0240] When the tip and the ring are implanted in a patient's heart, thetip will typically be embedded in the endocardial tissue, while the ringis situated in the right ventricle, in electrical contact with theendocardium via the ventricular blood. If the photonic catheter isconnected to a pacemaker, an optical pulse emanating from a photonicpacemaker pulsing unit (not shown) is sent down a fiber optic element orbundle of the photonic catheter. The fiber optic element or bundlepasses into the hermetically sealed interior of the ring via a hermeticseal terminal (460, 481, 512). There, the fiber optic element or bundledelivers the optical pulse to the component array, which preferablyincludes a photodiode array. The photodiode array produces an electricalimpulse that negatively drive the tip with respect to the ring at apotential of about 3-4 volts and a current level of about 3 milliampsfor a total power output of about 10 milliwatts. Note that a sensingfunction could be added by incorporating an electro-optical transducerinto the component array. Electrical sense signals would then beconverted to optical signals and placed on the fiber optic element orbundle for delivery to a sensing unit (not shown).

[0241]FIG. 54 illustrates an exemplary construction of the componentarray in which the array comprises a photodiode array 532 for receivingoptical pacing signals from the fiber optic element or bundle 525 and alight emitting diode 533 for delivering optical sensing signals to thefiber optic element or bundle. The components 532 and 533 are mounted ona circuit substrate 527 that is electrically connected to an electricalcircuit unit 534 that may include transducers, amplifiers, oscillators,a microprocessor, and other devices that can assist electrical pulsedelivery and biological sensing functions.

[0242]FIGS. 55 through 57 include a modified hermetic housing to providea unitary or integral electrode termination pair 540. The electrodetermination pair 540 includes a tip 539 and a ring 538 that areconstructed as metallic coatings formed on the hermetic housing (551,565).

[0243] An electrically conductive coating (552, 566) formed at thedistal end of the housing provides the tip. An electrically conductivecoating (547, 559) formed at the proximal end of the housing providesthe ring.

[0244]FIGS. 56 and 57 also show that the component array can behermetically sealed within the housing via the hermetic seal. Theproximal end of the housing may then be secured to the distal end of thephotonic catheter, and the fiber optic element or array can be connectedto the component array via the hermetic terminal. The component array iselectrically connected to the tip and the ring via electrical leads.

[0245]FIG. 58 shows an exemplary implementation of the component arraywithin the housing. This component array configuration is identical tothe component array configuration of FIG. 55.

[0246] In FIG. 59, a modified hermetic housing again provides a completeelectrode termination pair 586. The electrode termination pair 586includes a tip electrode 584 and a ring electrode 582 that areconstructed as electrically conductive band coatings on the hermetichousing, which is designated by reference numeral 581. A shallow well562 of FIG. 60 formed near the distal end of the housing 560 of FIG. 60may be used to mount the tip 561. A shallow well 593 of FIG. 60 formedtoward the proximal end of the housing 560 of FIG. 60 may be used tomount the ring 594 of FIG. 60.

[0247]FIG. 61 shows an exemplary implementation of the component arraywithin the housing. This component array configuration is identical tothe component array configuration of FIG. 54.

[0248] The output of a typical pacemaker is illustrated in FIG. 31,which is a graph of the electrical direct current voltage (vDC) appliedto the electrode or electrodes at the distal end of a cardiac pacemakerlead, as a function of time. The indicated voltage of 3 vDC is a nominalvalue and is typically often selected by the physician based on the typeof cardiac anomaly being corrected, the physical state of the patient'sheart, and other factors. However, it should be understood that thisvalue is intended to have a safety factor of two built into it; thus thetypical voltage required to pace the heart is 1.5 volts direct current,or less.

[0249] Referring again to FIG. 31, and noting that the time axis is notto scale, the typical time between pacing events is nominally onesecond, or 1000 milliseconds (mS). In normal practice, using modempacemakers, this time interval is not fixed but is variable based upontwo factors. The first factor is whether or not the heart requirespacing in order to beat. The term ‘demand pacemaker’ applies to a devicethat senses heart activity electrically and does not send a pacingsignal to the electrodes if the heart is beating on its own in a mannerdetermined to be acceptable by the computer controller within thedevice, and based upon input programmed by the physician. Thus, duringthe time after the refractory period associated with the previousheartbeat ends 321, and up to a time when the next heartbeat is required322, the pacemaker electrode is used to sense heart activity and todisable the next pacing signal 323 if the heartbeat is regular.

[0250] The second factor associated with demand pacing is physiologicdemand; modem pacemakers are designed with additional sensing andanalytical capability that permits the device to monitor physiologicdemand associated with physical activity or other forms of stress thatwould result in an elevated heartbeat in a normal human subject. Inresponse to this heightened physiologic demand, the pacing signal 323would be generated at an earlier time than the 1000 mS delay indicatedin FIG. 31.

[0251]FIG. 32 is an expanded view similar to FIG. 31, showing the pacingsignal 326 over the nominal one-millisecond time interval of the actualpacing signal. The beginning of the pacing signal (319, 324) and the endof the pacing signal (320, 325) are shown in both FIG. 31 and FIG. 32for reference. Note that there is no other activity in this onemillisecond time interval; more particularly there is no attempt tosense heart activity nor the heart's response to the pacing signalduring the time pacing time interval between times (319, 324) and (320,325). This is in part due to the fact that while a relatively modestvoltage (about 3 volts) is being applied to the heart cardiac tissue bythe electrodes, the voltages sensed by the pacemaker in monitoring heartactivity (typically in the millivolt range) would be immeasurable usingtraditional techniques. In addition, the tissues surrounding the pacingelectrode develop a polarization potential in response to the energy inthe pacing signal; this serves to make measurements of heart activityvia those same electrodes very difficult using traditional techniques.However, the interval between times (319, 324) and (320, 325) is verylong in the context of modem computational electronic devices.

[0252]FIGS. 33, 34, and 35 are schematic representations of a cardiacpacemaker lead (327, 329, 333) having various electrode configurations.

[0253] In one preferred embodiment, and referring to FIG. 33, pacemakerlead 327 comprises one or more electrical conductors communicating froma connector on the body of the pacemaker device (not shown) to theelectrodes 328 that are affixed by one of a number of techniques to thesensitive cardiac tissue that initiates the natural heartbeat and thatis paced when necessary by the implanted pacemaker system. Theconfiguration shown in FIG. 33 is for a bipolar pacemaker; the positiveand negative terminals for electron flow through the cardiac tissue arethe two electrodes 328. It should be noted that there is an alternativeconfiguration referred to as unipolar, and it is not shown in thisfigure. In the case of a unipolar configuration, there is a singleelectrode 328 at the heart; the return path for electron flow is throughthe general bulk tissue back to the case of the device itself. In eitherunipolar or bipolar configurations, electrodes 328 are used both to pacethe heart during the period between times (319, 324) and (320, 325)shown in FIGS. 31 and 32, but are also used to sense heart activityelectrically between times 321 and 322 shown in FIG. 31.

[0254] In the embodiment depicted in FIG. 34, sensing electrode 332 isdisposed at a distance of at least about 5 millimeters from pacingelectrode 330 in order to provide a degree of electrical isolationbetween tissues that will develop a polarization potential and tissuesbeing sensed for heartbeat activity. Similarly, in the embodimentdepicted in FIG. 35, sensing electrode pair 335 is disposed at adistance of at least about 5 millimeters from pacing electrode pair 334.

[0255] In another preferred embodiment, cardiac pacemaker lead is not anelectrical conductor but rather comprises one or more optical fibersthat carry light energy between the pacemaker device case and theelectrodes. This embodiment may be used in order to create pacemakerleads that are immune to the intense radio frequency and magnetic fieldsassociated with magnetic resonance imaging (MRI) and which fields can insome cases result in damage to the pacemaker and/or injury or death tothe pacemaker patient who inadvertently undergoes MRI diagnosis. In thisembodiment electrodes are more complex than in the former embodiment;for purposes of pacing they comprise a photodiode (not shown) used toconvert light energy to electrical energy within them, and in the caseof sensing cardiac activity they also comprise a miniature electricalamplifier and light emitting diode source that creates an optical signalthat travels from the electrode back to a pacemaker device that uses thephotonic catheter of this embodiment.

[0256] In another embodiment, and referring to FIG. 34, the pacemakerlead 329 connects the pacemaker device case (not shown) to a set ofelectrodes 330, 331, and 332 at its distal end and affixed to cardiactissue as in the previous embodiment. Electrode 331, as in the previousembodiment, is capable of either pacing the heart or sensing heartactivity electrically. Electrode 330 is used only to pace the heart, andis identical in its function to that part of the function of thedual-purpose electrode. In like manner electrode 332 is used only forsensing heart activity electrically, in a fashion identical to that partof the function of the dual-purpose electrode.

[0257] The reason for the configuration shown in FIG. 34 is that thecardiac tissue immediately involved in the pacing event, and whichdevelops a polarization potential as a result of the pacing signal, issomewhat removed physically from the cardiac tissue immediately aroundthe sensing electrode 332, thus providing some degree of isolation frompolarization potential in the area where cardiac sensing is being done,but still providing ample opportunity for sensing any cardiac activity.Thus this embodiment provides the opportunity for sensing measurementsto be made during dwell periods in the overall pacing signal wherein novoltage is being applied to the cardiac tissue.

[0258] In a further embodiment, and still referring to FIG. 34,pacemaker lead 329 does not contain electrical conductors but rathercomprises one or more optical fibers, as described in a previousembodiment. Likewise, electrodes 330 and 331 have the capability toconvert optical energy to electrical energy in order to pace the heart,and electrodes 331 and 332 comprise electrical amplifier andelectricity-to-light conversion, as is also described in the previousembodiment.

[0259] In yet another preferred embodiment, shown in FIG. 35, pacemakerlead 333 connects the pacemaker device case (not shown) to a set ofelectrodes 334 and 335 at its distal end and is affixed to cardiactissue as in the previous embodiments. In this embodiment, additionalseparation between the volume of cardiac tissue being paced (betweenelectrodes 334) and the volume of cardiac tissue being sensed (betweenelectrodes 335) is created in order to provide further improvements inelectrical isolation between those areas, thereby providing furtherimprovement in the ability to make sensing measurements during cardiacpacing.

[0260] In yet another embodiment, and still referring to FIG. 35,pacemaker lead 333 does not contain electrical conductors but rather oneor more optical fibers, as described in a previous embodiment. Likewise,electrodes 334 have the capability to convert optical energy toelectrical energy in order to pace the heart, and electrodes 335comprise electrical amplifier and electricity-to-light conversion asalso described in previous embodiments.

[0261] In one preferred embodiment of the present invention, a techniqueof pulsewidth modulation is used to pace the heart and to provide theopportunity for real-time measurement of cardiac tissue activity.

[0262] Referring to FIG. 36, it may be seen that a pacing signal 338that begins at time 341 is not a traditional square wave pulse as shownin FIGS. 31 and 32, but is a series of much faster pulses that apply avoltage 337 for a time period 339 and that apply no voltage during timeperiod 340.

[0263] For example, if time period 339 is chosen to be two microsecondsand if time period 340 is chosen to be one microsecond, a single repeatof sequence 339 and 340 has a duration of three microseconds. If thissequence is repeated three hundred thirty-three times, the time intervalfor pulse 338 will be about one millisecond, corresponding to the timeinterval of a single traditional pacing signal to the heart. Forpurposes of this illustrative example and again referring to FIG. 36,voltage 337 may be chosen to compensate for the fact that no voltage isapplied for one third of the time. In order for a pulsewidth signal 338having 66% duty cycle as described in this illustration to deliver thesame amount of electrical energy to the cardiac tissue as in a squarewave 3 volt DC pulse of 1 millisecond duration, and taking intoconsideration the relationship of energy to voltage in a purelyresistive medium (energy is proportional to the square of the appliedvoltage), the voltage 337 will be chosen to be 3 volts DC multiplied bythe square root of 1.5, or 3.67 volts direct current. If the frequencyof pulsewidth modulated pacing curve 338 is high with respect to thereaction time of cardiac tissue, that tissue will react in the samemanner to the pulsewidth modulated signal having 66% duty cycle and 3.67volt peak signal level as it would to a square wave of the same durationat 3.0 volt.

[0264] The foregoing example is intended to be illustrative only; in theembodiment depicted, time periods 339 and 340 may range from below 1microseconds to over 100 microseconds in order to optimize the responseof the system to design choices in the pacemaker device or the pacemakerlead and electrodes. In addition, this embodiment provides for timeperiods 339 and 340 to be variable over time, both in absolute durationand in their ratio. Further, the applied voltage 337 may be variableover time within a single pacing signal 338, or between pacing signals,as a function of changes in physiologic demand or based on changes inprogrammed response of the pacemaker system. For purposes of thisspecification, the overall signal that spans between times 339 and 340will be referred to as the pacing signal, the shorter signals sent tothe heart in multiples will be referred to as pulses, and the muchshorter signals described in this illustrative example as having timeduration 339 will be referred to as micropulses.

[0265] Referring once again to FIG. 36, it may be seen that a cardiactissue sensing measurement 343 may be carried out during time period342. In one embodiment, time period 342 may occur any time during thepacing signal and may have any duration appropriate to making saidsensing measurement. In a preferred embodiment, time period 342 isselected to be shorter in duration than time period 340, and is furthersynchronized so as to fall within time period 340. The result is thatthe electrical measurement of cardiac tissue activity is done during atime period wherein there is not pacing signal applied to the tissue.

[0266] Referring again briefly to FIGS. 33, 34, and 35, it may be seenthat in combination with the placement of electrodes on pacemaker leadthat provides isolation between the tissue being paced and the tissuebeing sensed, the additional temporal isolation of sensing period fromthe active time period of the pulsewidth modulated pacing signal, ameans is provided to measure the onset of cardiac response to the pacingsignal while the signal is still being generated as a set of multipleshorter pulses.

[0267]FIG. 37 is a graph depicting the operation of one preferredembodiment that gains energy efficiency by means of early termination ofthe pacing signal, but which uses a constant voltage applied to themicropulses comprising the pacing signal. The peak voltage of pulsesthat make up pacing signal 345 rises from zero to voltage 344 at time346, as previously shown in FIG. 36. At time 348, when a signal fromheart causes cessation of the micropulsing process, the pulsewidthpacing signal 345 returns to zero until the next pacing signal iscommanded from the demand controller. The area 347 depicts theadditional signal that a traditional pacemaker not practicing pulsewidthpacing would send to pace the heart after the onset of a beat at time348. As discussed previously, standard clinical practice calls for athreefold safety factor in pulse duration; employing a pacemaker in amanner depicted in FIG. 37, would result in up to approximately a 65percent reduction in energy consumption for the pacemaker system.

[0268]FIG. 38 is a graph depicting the operation of another preferredembodiment that gains energy efficiency by means of both earlytermination of the pacing signal and by the additional use of gradientpulsewidth power control. As in the previous embodiment, pulsewidthpacing signal 352 begins to rise from zero at time 353, and the voltageof each of the micropulses rises with each micropulse cycle. FIG. 38depicts a linear rise with time, but experimentation may result in adifferent algorithm that better matches the electrochemistry of cardiactissue; thus FIG. 38 should be considered as illustrative of a varietyof waveforms that may be employed to excite the heart. At time 354, whena signal from heart causes cessation of the micropulsing process, thepulsewidth pacing signal 352 returns to zero until the next pacingsignal is commanded from the demand controller. As in the example ofFIG. 37, the area 356 depicts the signal that a traditional pacemakernot practicing pulsewidth pacing would send to pace the heart.

[0269] As discussed previously, standard clinical practice calls for athreefold safety factor in pulse duration. The typical twofold safetyfactor in applied voltage results in a power level that is four timeshigher than the minimum to pace the specific patient's heart. Thus incombination the joint safety factors applied to voltage and pulseduration result in an energy utilization that is twelve times higherthan the minimum needed to reliably pace that individual's heart. Bypracticing pulsewidth pacing, which permits the cessation of thepulsewidth pacing signal virtually the instant the heart begins to beat,the energy consumption of a pacemaker may be reduced by as much as 90%.

[0270] It should also be understood that in using a pulsewidthmodulation control technique, it is not necessary to alter the actualpeak voltage of the pulses that make up the pacing signal to effect anapparent change in applied voltage. If the frequency of the pulses ishigh enough in comparison to the response time of the circuit and thecardiac tissue through which the pacing signal is conducted, the tissuewill react in the same manner as if the applied voltage were the actualpeak voltage multiplied by the duty cycle. Thus, the electronic circuitmay be designed to utilize a single voltage and adjust duty cycle byadjusting the ratio of times 339 and 340. This permits optimization theenergy efficiency of power sources and switching circuits.

[0271]FIG. 39 depicts an alternative overall waveform for pacing signal360. Note that for reasons of simplicity the overall value of peakvoltage is shown for pacing signal 360, and not the individualpulsewidths, as shown in FIG. 38. However, this embodiment still makesuse of the high-frequency pulsewidth approach shown in greater detail inFIGS. 37 and 38. Whereas FIG. 38 depicts a linear rise with time, FIG.39 depicts an initial rise of pacing signal 360 at time 361 from 0 vDCto voltage 359, followed by a nonlinear increase to voltage 358, atwhich time 362 a heartbeat has been sensed, and pacing signal 360 is cutoff as in the previous embodiments described herein.

[0272] Experimentation may result in a different algorithm that bettermatches the electrochemistry of cardiac tissue, and this algorithm maybe developed for the specific patient during the initialpost-implantation period. Thus, FIGS. 38 and 39 should be considered asillustrative of a variety of waveforms that may be employed to excitethe heart, and may be made specific to the needs of each pacemakerpatient.

[0273] As in the previous embodiment depicted in FIG. 38, the use ofpulsewidth modulation techniques in the embodiment depicted in FIG. 39permits optimization of energy efficiency by adjusting duty cycle ratherthan adjusting actual peak voltage.

[0274] The photonic catheter described above may be used fortransmission of a signal to and from a body tissue of a vertebrate. Thefiber optic bundle has a surface of non-immunogenic, physiologicallycompatible material and is capable of being permanently implanted in abody cavity or subcutaneously. The fiber optic bundle has a distal endfor implantation at or adjacent to the body tissue and a proximal end.The proximal end is adapted to be coupled to and direct an opticalsignal source, and the distal end is adapted to be coupled to an opticalstimulator. The fiber optic bundle delivers an optical signal intendedto cause an optical stimulator coupled to the distal end to deliver anexcitatory stimulus to a selected body tissue, such as a nervous systemtissue region; e.g., spinal cord or brain. The stimulus causes theselected body tissue to function as desired.

[0275] The photonic catheter further includes a photoresponsive devicefor converting the light transmitted by the fiber optic bundle intoelectrical energy and for sensing variations in the light energy toproduce control signals. A charge-accumulating device receives andstores the electrical energy produced by the photoresponsive device. Adischarge control device, responsive to the control signals, directs thestored electrical energy from the charge-accumulating device to acardiac assist device associated with a heart.

[0276] The photoresponsive device may include a charge transfer controlcircuit and a photodiode. The charge transfer control circuit controls adischarging of a photodiode capacitance in two separate dischargeperiods during an integration period of the photodiode such that a firstdischarge period of the photodiode capacitance provides the sensing ofvariations in the light energy to produce control signals and a seconddischarge period of the photodiode capacitance provides the convertingthe light transmitted by the photonic lead system into electricalenergy. The first discharge period can be a shorter time duration thatthe time duration of the second discharge period. During the firstdischarge period, a control signal sensing circuit is connected to thephotodiode, and during the second discharge period, thecharge-accumulating device is connected to the photodiode. Thecharge-accumulating device may be a capacitor or a rechargeable battery.

[0277] The photonic catheter can also transmit between the primarydevice housing and the cardiac assist device, both power and controlsignals in the form of light. A photoresponsive device converts thelight transmitted by the photonic lead system into electrical energy andto sense variations in the light energy to produce control signals. Acharge-accumulating device receives and stores the electrical energyproduced by the photoresponsive device, and a discharge control device,responsive to the control signals, directs the stored electrical energyfrom the charge-accumulating device to the cardiac assist deviceassociated with the heart.

[0278] The photoresponsive device, in this embodiment, may include acharge transfer control circuit and a photodiode. The charge transfercontrol circuit controls a discharging of a photodiode capacitance intwo separate discharge periods during an integration period of thephotodiode such that a first discharge period of the photodiodecapacitance provides the sensing of variations in the light energy toproduce control signals and a second discharge period of the photodiodecapacitance provides the converting the light transmitted by thephotonic lead system into electrical energy. The first discharge periodcan be a shorter time duration that the time duration of the seconddischarge period. During the first discharge period, a control signalsensing circuit is connected to the photodiode, and during the seconddischarge period, the charge-accumulating device is connected to thephotodiode. The charge-accumulating device may be a capacitor or arechargeable battery.

[0279] The physical realization of the photodiode functions aslight-detecting elements. In operation, the photodiode is first resetwith a reset voltage that places an electronic charge across thecapacitance associated with the diode. Electronic charge, produced bythe photodiode when exposed to illumination, causes charge of thephotodiode capacitance to dissipate in proportion to the incidentillumination intensity. At the end of an exposure period, the change inphotodiode capacitance charge is collected as electrical energy and thephotodiode is reset.

[0280] Manipulating or adjusting the charge integration function of thephotodiode can modify the creation of energy by the sensors. Chargeintegration function manipulation can be realized by changing of anintegration time, T_(int), for the photodiode. Changing the integrationtime, T_(int), changes the start time of the charge integration period.

[0281] Integration time, T_(int), is the time that a control signal isnot set at a reset level. When the control signal is not at a resetvalue, the photodiode causes charge to be transferred or collectedtherefrom. The timing of the control signal causes charge to betransferred or collected from the photodiode for a shorter duration oftime or longer duration of time. This adjustment can be used to managethe charge in the photodiode so that the photodiode does not becomesaturated with charge as well as to manage the current output of thesensor.

[0282] Another conventional way of manipulating the charge integrationfunction is to use a stepped or piecewise discrete-time chargeintegration function. By using a stepped or piecewise discrete chargeintegration function, the charge in the photodiode can be furthermanaged so that the photodiode does not become saturated with charge aswell as to manage the current output of the photodiode.

[0283] The photonic catheter can also be used to measure displacementcurrent. Unlike a standard conduction current of moving electrons,displacement current is a measure of the changing electric field in theair, generated by the shifting voltages on the skin surface. Toaccurately measure this subtle current in the air without shorting it, asensor is needed with impedance higher than that of the air gap betweenthe body and the sensor. Otherwise, the sensor will drain the electricalsignal just like an ECG contact sensor does. The sensor can be a smallcopper disc about a centimeter across, which can produce sensitive ECGs.

[0284] As illustrated in FIGS. 66-69, a photonic catheter 585 maycontain a sensor to detect the presence of MRI insult. Mostspecifically, the photonic catheter 585 may include at a distal end alogic and control circuit 586 connected to an amplifier 587. Theamplifier 587 may be connected to a single MRI coil as illustrated inFIG. 66 or to multiple MRI coils (589, 590, 591 . . . ) as illustratedin FIG. 67. In FIG. 68, the MRI insult sensor is encased in a sleeve 592that enables the MRI coil 592 to be rotatable within the photoniccatheter 585. Lastly, the photonic catheter 585, as illustrated in FIG.69, may position two MRI coils 593 and 594 at predetermined angles β toeach other, such as 90°. The MRI coils are located in the distal end ofthe photonic catheter and detects characteristics of magnetic radiationof a predetermined nature. Each coil may be designed to detect adifferent type of radiation.

[0285]FIG. 21 illustrates an optical transducer including a pressuresensor 225 in a porous non-conductive insert 226 that is coupled to aphotonic catheter or other optical communication channel.

[0286]FIG. 22 illustrates in more detail, the pressure opticaltransducer device of FIG. 21. In FIG. 22, an optical transducer deviceis anchored to a predetermined tissue region 230, such as a cardiacmuscle region, by anchors 227 and 229. The anchors are connected to aporous sleeve 231 that houses a pressure sensor 228. The opticaltransducer device further includes a mechanical-optical transducer 232,within housing 233, to produce an optical signal corresponding to themovement of pressure sensor 228. Pressure sensor 228 moves back andforth in response to pressure generate by contractions of thepredetermined tissue region 230. Based on the pressure gradientproduced, the pressure sensor 228 will move and cause themechanical-optical transducer 232 to produce a signal containinginformation on the characteristics of the predetermined tissue region230.

[0287] In FIG. 23, an optical transducer device is anchored to apredetermined tissue region 234, such as a cardiac muscle region, by aporous sleeve 235 that houses a pressure sensor 236. The opticaltransducer device further includes a mechanical-optical transducer 239,within housing 237 and connected to optical cable 238, to produce anoptical signal corresponding to the movement of pressure sensor 236.Pressure sensor 236 moves back and forth in response to pressuregenerate by contractions of the predetermined tissue region 234. Basedon the pressure gradient produced, the pressure sensor 236 will move andcause the mechanical-optical transducer 239 to produce a signalcontaining information on the characteristics of the predeterminedtissue region 234.

[0288] In FIG. 24, an optical transducer device is anchored to apredetermined tissue region 240, such as a cardiac muscle region, by aporous sleeve 241 that houses an optical device 242. The optical device242 produces an optical signal that reflects off the predeterminedtissue region 240. Based upon the nature of the reflection, opticaldevice 242 produces optical signals corresponding to the characteristicsof the predetermined tissue region 240. These optical signals aretransmitted over an optical cable 244 within a housing 243.

[0289] In FIG. 25, an optical transducer device for a cardiac region isillustrated. An optical device 251 produces light that is fed alongfiber optics 247 and 250 to a ventricle area of the heart and an atriumarea of the heart, respectively. The light is reflected off these areasand fed back to the optical device 251 through fiber optics 248 and 249.Based upon the nature of the reflection, optical device 251 producesoptical signals corresponding to the characteristics of the monitoredareas. These optical signals 252 are transmitted over an optical cable253 to a control unit device 254 at a proximal end of the optical cable253.

[0290]FIG. 26 illustrates one embodiment of an optical sensor. In FIG.26, a fiber optic bundle 258 includes individual fiber optics 259. Oneof the fiber optics produces the reference light that is reflected offflap 261 within the optical sensor. The flap 261 will move between stops257 and 260 based on characteristics within a predetermined tissueregion. As the flap 261 moves on pivot 262, the light is reflected atdifferent angles and thus is collected by a different fiber in the fiberoptic bundle, depending upon the angle of reflection. In this way, thecharacteristics of the predetermined tissue region can be measured.

[0291]FIGS. 63 and 64 illustrate one embodiment of an optical sensor1008. In FIGS. 63 and 64, a fiber optic bundle 1017 includes individualfiber optics 1013 and 1016. One of the fiber optics 1013 produces thereference light that is reflected off flap 1014 within the opticalsensor 1008. The flap 261 will move based on muscle contractions ofmuscle tissue 1018 and 1020 in a predetermined tissue region that iswithin the optical sensor 1008 through openings 1010 and 1012. As theflap 1014 moves on pivot 1015, the light is reflected at differentangles and thus is collected by a different fiber 1016 in the fiberoptic bundle, depending upon the angle of reflection. In this way, thecharacteristics of the predetermined tissue region can be measured.

[0292]FIG. 62 is an optical sensor and stimulation device 1030 for aphotonic catheter. In FIG. 62, the optical sensor and stimulation device1030 includes a ring electrode 1034 and a tip electrode 1032 to sense orstimulate a predetermined tissue region. The ring electrode 1034 and atip electrode 1032 are connected to a control circuit 1038 that producesenergy to enable the ring electrode 1034 and tip electrode 1032 tostimulate the predetermined tissue region or enables the ring electrode1034 and tip electrode 1032 to sense characteristics of thepredetermined tissue region. Control signals from a proximal end arecommunicated along a fiber optic 1044 and received by sensor 1040.Sensor 1040 also receives other light signals over channel 1044 that isconverted into electrical energy to be stored for later use. The sensedcharacteristics of the predetermined region are transmitted by device1008 over fiber optic 1017 to the proximal end.

[0293]FIG. 65 illustrates a pressure pulse sensor 580. Cardiac tissuecauses a mirror membrane to be at position 578 when the heart is in thediastolic interval because the pressure from the cardiac tissuedecreases and in position 579 when the heart is in the systolic intervalbecause the pressure from the cardiac tissue increases. When the mirrormembrane is in position 579, laser light 581 from fiber optic 583 isreflected along ray 582 to fiber optic sensor 584. The pressure istransferred to the pressure pulse sensor 580 through openings 576 and577.

[0294] Alternatively to the electromagnetic insult immune systemsdescribed above, a system can avoid failure during magnetic resonanceimaging by determining a quiet period for a tissue implantable deviceand generating a magnetic resonance imaging pulse during a quiet periodof the tissue implantable device. Moreover, a system can avoid failuredue to an external electromagnetic field source by detecting a phasetiming of an external electromagnetic field or external magneticresonance imaging pulse field and altering operations of the tissueimplantable device to avoid interfering with the detected externalelectromagnetic field or external magnetic resonance imaging pulsefield. In these instances the tissue implantable device may be a cardiacassist device.

[0295] The concepts of the present invention may also be utilized in anelectromagnetic radiation immune tissue invasive delivery system. Theelectromagnetic radiation immune tissue invasive delivery system has aphotonic lead having a proximal end and a distal end. A storage device,located at the proximal end of the photonic lead, stores a substance tobe introduced into a tissue region. A delivery device delivers a portionof the stored substance to a tissue region. A light source, in theproximal end of the photonic lead, produces a first light having a firstwavelength and a second light having a second wavelength.

[0296] A wave-guide is located between the proximal end and distal endof the photonic lead. A bio-sensor, in the distal end of the photoniclead, senses characteristics of a predetermined tissue region, and adistal sensor, in the distal end of the photonic lead, converts thefirst light into electrical energy and, responsive to the bio-sensor, toreflect the second light back the proximal end of the photonic lead suchthat a characteristic of the second light is modulated to encode thesensed characteristics of the predetermined tissue region. A proximalsensor, in the proximal end of the photonic lead, converts the modulatedsecond light into electrical energy, and a control circuit, in responseto the electrical energy from the proximal sensor, controls an amount ofthe stored substance to be introduced into the tissue region.

[0297] In this embodiment, the sensed characteristic may be an EKGsignal, a glucose level, hormone level, or cholesterol level. The storedsubstance may be a cardiac stimulating substance, a blood thinningsubstance, insulin, estrogen, progesterone, or testosterone.

[0298] The MRI compatible photonic catheter, according to the conceptsof the present invention, can also be utilized to illuminate a multiplesector photodiode, whose sectors are electrically connected in series sothat the voltage output of each sensor is additive, thereby producing atotal output voltage in excess of what would be achieved from a singlesensor.

[0299] In another embodiment of the present invention, a higher voltageand current outputs is achieved by increasing the number and size ofdetectors. This embodiment also provides very accurate and stablealignment of the radiation wave-guide to the sensor, and a uniformspatial intensity of the output beam that illuminates the multiplesensor sectors.

[0300] An example of a MRI compatible photonic catheter being utilizedto transfer power or energy to a tissue region located at a distal endof the catheter is illustrated in FIG. 70. FIG. 70 shows a wave-guide2001 coupled to a radiation source (not shown). The wave-guide 2001directs radiation into a radiation scattering medium 2007. Attached tothe surface of the radiation scattering medium 2007 are multipleradiation sensors 2010-2013, mounted along the axis of scattering medium2007, for receiving and converting incident radiation into electricalenergy. The multiple radiation sensors 2010-2013 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor.

[0301] The physical realization of the sensors is either a plurality ofphototransistors or a plurality of photodiodes functioning aslight-detecting elements. In operation, the sensor is first reset with areset voltage that places an electronic charge across the capacitanceassociated with the diode. Electronic charge produced by, for example, aphotodiode, when exposed to illumination, causes charge of the diodecapacitance to dissipate in proportion to the incident illuminationintensity. At the end of an exposure period, the change in diodecapacitance charge is collected as electrical energy and the photodiodeis reset.

[0302] Manipulating or adjusting the charge integration function of thesensor can modify the creation of energy by the sensors. Chargeintegration function manipulation can be realized by changing of anintegration time, T_(int), for the sensor. Changing the integrationtime, T_(int), changes the start time of the charge integration period.

[0303] Integration time, T_(int), is the time that a control signal isnot set at a reset level. When the control signal is not at a resetvalue, the sensor causes charge to be transferred or collectedtherefrom. The timing of the control signal causes charge to betransferred or collected from the sensor for a shorter duration of timeor longer duration of time. This adjustment can be used to manage thecharge in the sensor so that the sensor does not become saturated withcharge as well as to manage the current output of the sensor.

[0304] Another conventional way of manipulating the charge integrationfunction is to use a stepped or piecewise discrete-time chargeintegration function. By using a stepped or piecewise discrete chargeintegration function, the charge in the sensor can be further managed sothat the sensor does not become saturated with charge as well as tomanage the current output of the sensor.

[0305] The radiation scattering medium 2007 and multiple sensors2010-2013 are mounted such that there is little or no surface of thescattering medium that is not covered by a sensor. Any areas that arenot covered by sensors are preferably covered with an internallyreflective coating that directs incident radiation back into thescattering medium 2007 for absorption by the sensors 2010-2013. Togetherthese features ensure that the sensors 2010-2013 absorb a maximum amountof radiation.

[0306] In FIGS. 71 and 72, multiple sensors 2021-2026 are alternatelymounted circumferentially along the periphery of the scattering medium2007, for receiving and converting incident radiation into electricalenergy. The multiple radiation sensors 2021-2026 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor.

[0307] In FIG. 73, radiation scattering medium 2031-2034 with adecreasing radiation transmission rate along the axis of the medium2031-2034 is used. A scattering medium 2031-2034 with these propertieswould be used when sensors 2035-2038 are electrically connected inseries with consecutive sensors in the electrical circuit placed furtheralong the axial direction of the scattering medium. This feature ensuresthat each sensor receives an equal exposure of radiation, produces asimilar output current, thereby ensuring that the output current of theseries circuit including all sensors is not limited by the outputcurrent of any individual sensor due to limited incident radiation.

[0308] In FIG. 74, multiple sensors 2041-2044 of varying size along theaxis of the scattering medium 2007 are used. By placing larger sensorstowards the distal end of the scattering medium 2007, these sensors2043-2044 receive an exposure of radiation equal to more proximallypositioned sensors 2041-2042 and therefore produce equivalent outputcurrents, even though the radiation intensity at the distal end of thescattering medium 2007 may be less than the radiation intensity at theproximal end of the scattering medium 2007.

[0309] In FIG. 75, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation into a second wave-guide 2054 withmultiple radiation beam splitters 2050-2053 located along the opticalaxis of the wave-guide. Attached to the second wave-guide 2054 aremultiple radiation sensors 2045-2048, mounted along the axis of thewave-guide 2054, for receiving and converting incident radiation intoelectrical energy. The multiple radiation sensors 2045-2048 areelectrically connected in series so that the voltage output of eachsensor is additive, thereby producing a total output voltage in excessof what would be achieved from a single sensor. The multiple sensors2045-2048 are mounted such that there is little or no surface of thesecond wave-guide 2054 that is not covered by either a sensor orinternally reflective coating. Together these features ensure that thesensors 2045-2048 absorb a maximum amount of radiation.

[0310] In FIG. 76, a second wave-guide 2059 with beam splitters thathave decreasing radiation transmission rates along the axis of themedium 2059 is used. This feature would be used when sensors 2055-2058are electrically connected in series with consecutive sensors in theelectrical circuit placed further along the axial direction of thewave-guide 2059. Each sensor receives an equal exposure of radiation andproduces a similar output current, thereby ensuring that the outputcurrent of the series circuit including all sensors is not limited bythe output current of any individual sensor due to limited incidentradiation.

[0311] In FIG. 77, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation onto a stack of sensors 2061-2064 suchthat each sensor absorbs a fraction of radiation incident upon thestack. The multiple radiation sensors 2061-2064 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor. To ensure maximum current outputof the series circuit containing all sensors 2061-2064, the radiationcapture is increased with increasing distance into the sensor stack,which can be accomplished in several ways, including increasing sensorthickness that reduces radiation transfer through the consecutivesensors.

[0312] In FIG. 78, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation onto a concentrically oriented array ofsensors 2071-2073. Multiple radiation sensors 2071-2073 are electricallyconnected in series so that the voltage output of each sensor isadditive, thereby producing a total output voltage in excess of whatwould be achieved from a single sensor. Each sensor has an equal area toensure equal radiation exposure to all sensors 2071-2073, therebyproducing maximum current output for the series connected sensor array.This embodiment would be used when it is desirable to over-illuminatethe sensor array to ensure equal radiation exposure to all sensors.

[0313] In FIG. 79, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation onto a reflective grating 2084 thatdisperses radiation uniformly over the surface of multipleconcentrically located sensors 2081-2083. The multiple radiation sensorsare electrically connected in series so that the voltage output of eachsensor is additive, thereby producing a total output voltage in excessof what would be achieved from a single sensor.

[0314] In FIG. 80, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation onto a single radiation sensor 2091 thatis connected to multiple capacitors (C₁, C₂, C₃, . . . , C_(n))electrically connected in parallel, enabling simultaneous charging ofthe capacitors (C₁, C₂, C₃ . . . , C_(n)) by the output voltage of thesingle sensor 2091. The voltage of each capacitor is controlled by theduration of the single pulse of radiation incident upon the singlesensor. In FIG. 81, the charged capacitors (C₁, C₂, C₃, . . . , C_(n))are switchable to a series electrical circuit so that the voltage outputof each capacitor is additive, thereby producing a total output voltagein excess of what would be achieved from a single capacitor.

[0315] In FIG. 82, a catheter features a solid-state control circuit2094 to manage capacitor charging, switching, and discharging functions,as well as other distal control functions. The control circuit 2094 ispowered by electrical energy supplied by the illuminated sensor 2091.Additional features of this illustrated catheter include a housing andpacing electrodes 2093 and 2095.

[0316] Variable capacitance capacitors can be utilized that are tuned toprecisely match individual capacitor capacitances, thereby providingextraordinary control over output voltage and power.

[0317] In FIGS. 81 and 82, the parallel electrical circuit ensures thateach capacitor is charged to the same voltage level, ensuring apredictable output voltage when the parallel charged capacitors areconnected in series and discharged. Moreover, the absence of multiplesensor sectors ensures that spatial variation in illumination intensitybetween sectors will not minimize the current of any one sector andthereby the entire circuit. Furthermore, the total energy dissipated bythe series connected electrical circuit is determined by parameters thatare easy to control; such as, the pre-selected capacitance of thecapacitors (Power=CV²/2), as well as the intensity and duration of theradiation pulse and duration of the discharge pulse which are controlledby the solid state control circuit. The diameter of the single sensor2091 is limited only by the size of the radiation wave-guide 2001.Lastly, reliability is improved due to reduced switching operations.

[0318] In FIG. 83, a wave-guide 2001 is coupled to a radiation source(not shown) to direct radiation onto a single radiation sensor 2091 thatis sequentially connected to multiple capacitors (C₁, C₂, C₃, . . . ,C_(n)) for charging. The voltage of each capacitor is controlled by theduration of the radiation pulse incident upon the surface of the singlesensor 2091.

[0319] In FIG. 84, the capacitors (C₁, C₂, C₃, . . . , C_(n)) aresubsequently connected in series for discharging, thereby producing atotal output voltage in excess of what would be achieved from a singlesensor or single capacitor. A solid-state control circuit (not shown) isutilized to manage capacitor charging, switching, and dischargingfunctions, as well as other distal control functions. The controlcircuit is powered by electrical energy supplied by the sensor 2091.

[0320] The electrical measurements of the charging characteristics ofeach capacitor are determined prior to utilizing the catheter. Thiscalibration information is then pre-programmed into a proximally locatedcontrol circuit to determine the duration and intensity of the radiationpulse required to achieve a specific voltage across the capacitor,thereby providing a predictable output voltage when the parallel chargedcapacitors are connected in series and discharged.

[0321] In FIGS. 83 and 84, the sequentially charging electrical circuitenables each capacitor to be charged with a pre-determined pulseintensity and duration, ensuring a predictable output voltage when theparallel charged capacitors are connected in series and discharged. Theabsence of multiple sensor sectors ensures that spatial variation inillumination intensity between sectors will not minimize the current ofany one sector and thereby the entire circuit. Furthermore, the totalenergy dissipated by the series connected electrical circuit isdetermined by parameters that are easy to control; such as, thepre-selected capacitance of the capacitors (Power=CV²/2), as well as theintensity and duration of the radiation pulse and duration of thedischarge pulse which are controlled by the solid state control circuit.The diameter of the sensor 2091 is limited only by the size of theradiation wave-guide 2001.

[0322] In FIG. 85, the output energy of a single radiation source 3001is split into multiple beams by radiation beam splitter 3006 havingmultiple beam splitters 3002-3005 and directed into multiple wave-guides3007-3010 to direct radiation onto multiple radiation sensors 3011-3013.Redundant sensors 3011-3013 are connected in series to produce a totaloutput voltage in excess of what would be achieved from a single sensor.

[0323] Power transfer can also be realized by a radiation source coupledto a wave-guide to direct radiation onto a single radiation sensor. Thisphotonic system design is repeated with additional radiation sources,additional wave-guides, and additional radiation sensors. Redundantsensors are connected in series to produce a total output voltage inexcess of what would be achieved from a single sensor.

[0324] These embodiments may also utilize a variable intensity radiationsource that can be used to vary the output current of the seriesconnected sensors. Moreover, this embodiment may include a controlcircuit that controls the period and nature of the charge integrationfunction of the sensors to maximize the output current of the sensors.

[0325] It is noted that the power transfer embodiments illustrated inFIGS. 70-85 can be combined with the photonic sensing embodimentsillustrated in FIGS. 5-20 such that the photonic catheter has both powertransfer and sensing capabilities.

[0326] The concepts of the present invention may also be utilized inimplanted insulin pumps. Implanted insulin pumps typically consist oftwo major subsystems: a pump assembly for storing and metering insulininto the body, and a sensor for measuring glucose concentration. The twoassemblies are typically connected by a metallic wire lead encased in abiocompatible catheter. The pump and sensor assemblies are typicallylocated in separate locations within the body to accommodate the largersize of the reservoir and pump assembly (which is typically located inthe gut), and to enable the sensor (typically located near the heart) tomore accurately measure glucose concentration.

[0327] The output of the sensor is delivered to the reservoir and pumpassembly as a coded electrical signal where it is used to determine whenand how much insulin to deliver into the body. The fact that the leadconnecting the two assemblies is a wire lead makes it susceptible tointerference from external magnetic fields, particularly the intensemagnetic fields used in MRI imaging. Interference from MRI fields caninduce electrical voltages in the leads that can damage the pumpassembly and cause incorrect operation of the pump which could lead topatient injury possibly even death.

[0328] Induced electrical currents can also cause heating of the leadthat can also damage the pump and cause incorrect operation of the pumpand injury to the patient due to pump failure as well as thermogenicinjury to internal tissues and organs. Shielding of the reservoir andpump assembly and sensor assembly can reduce direct damage to thesedevices, but cannot prevent induced electrical voltages and currentsfrom interfering with and damaging the devices.

[0329] According to the concepts of the present invention, a photoniclead replaces the metallic wire connecting the reservoir and pumpassembly and sensor assembly with a wave-guide such as an optical fiber.The sensor assembly is also modified to include means to transduce theelectrical signal generated by the sensor into an optical signal that isthen transmitted to reservoir and pump assembly over the wave-guide.This transduction means can be achieved by various combinations ofoptical emitters, optical attenuators, and optical sensors located ineither the sensor assembly or reservoir and pump assembly.

[0330] As noted above, the present invention is an implantable devicethat is immune or hardened to electromagnetic insult or interference.

[0331] In one embodiment of the present invention as illustrated in thefigures, an implantable pacemaker or a cardiac assist system is used toregulate the heartbeat of a patient. The implantable cardiac assistsystem is constructed of a primary device housing that has controlcircuitry therein. This control circuitry may include a control unitsuch a microprocessor or other logic circuits and digital signalprocessing circuits. The primary device housing may also include anoscillator, memory, filtering circuitry, an interface, sensors, a powersupply, and/or a light source.

[0332] The microprocessor may be an integrated circuit for controllingthe operations of the cardiac assist system. The microprocessorintegrated circuit can select a mode of operation for the cardiac assistsystem based on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

[0333] The primary device housing also can contain circuitry to detectand isolate crosstalk between device pulsing operations and devicesensing operations, a battery power source and a battery power sourcemeasuring circuit. In such an embodiment the microprocessor integratedcircuit can automatically adjust a value for determining an electivereplacement indication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

[0334] The microprocessor integrated circuit can be programmable from asource external of the cardiac assist system and can providephysiological or circuit diagnostics to a source external of the cardiacassist system.

[0335] The microprocessor integrated circuit may also include adetection circuit to detect a phase timing of an externalelectromagnetic field. The microprocessor integrated circuit alters itsoperations to avoid interfering with the detected externalelectromagnetic field. Moreover, the cardiac assist system would includesensors may detect a heart signal and to produce a sensor signaltherefrom and a modulator to modulate the sensor signal to differentiatethe sensor signal from electromagnetic interference or a samplingcircuit to sample the sensor signal multiple times to differentiate thesensor signal from electromagnetic interference, undesirable acousticsignals, large muscle contractions, or extraneous infrared light.

[0336] The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

[0337] The cardiac assist system also includes a lead system to transmitand receive signals between a heart and the primary device housing. Thelead system may be a fiber optic based communication system, preferablya fiber optic communication system contains at least one channel withina multi-fiber optic bundle, or the lead system may be a plurality ofelectrical leads. The lead system is coated with electromagneticinterference resistant material.

[0338] With respect to the electrical lead system, the plurality ofelectrical leads has a second shielding therearound, the secondshielding preventing the electrical leads from conducting strayelectromagnetic interference. The second shielding can be a metallicsheath to prevent the electrical leads from conducting strayelectromagnetic interference; a carbon composite sheath to prevent theelectrical leads from conducting stray electromagnetic interference; ora polymer composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference. The electrical leads mayeither be unipolar, bipolar or a combination of the two. Moreover, thelead system itself may be a combination of fiber optic leads andelectrical leads wherein these electrical leads can be either unipolar,bipolar or a combination of the two.

[0339] The lead systems may include a sensing and stimulation system atan epicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

[0340] Although the leads may be fiber optic strands or electrical leadswith proper shielding, the actual interface to the tissue, theelectrodes, cannot be shielded because the tissue needs to receive thestimulation from the device without interference. This causes theelectrodes to be susceptible to electromagnetic interference or insult,and such insult can cause either damage to the tissue area or thecircuitry at the other end. To realize immunity from the electromagneticinterference or insult, each electrode has an anti-antenna geometricalshape. The anti-antenna geometrical shape prevents the electrode frompicking up and conducting stray electromagnetic interference.

[0341] Moreover, the primary device housing, may include for redundancyfiltering circuits as the ends of the electrical leads at the primaryhousing interface to remove stray electromagnetic interference from asignal being received from the electrical lead. The filters may becapacitive and inductive filter elements adapted to filter outpredetermined frequencies of electromagnetic interference.

[0342] In addition to the electromagnetic interference shielding, theprimary device housing, and lead system, whether it is a fiber opticsystem or electrical lead system can be coated with a biocompatiblematerial. Such a biocompatible material is preferably a non-permeablediffusion resistant biocompatible material.

[0343] In another embodiment of the present invention as illustrated inthe figures, an implantable pacemaker or a cardiac assist system is usedto regulate the heartbeat of a patient. The implantable cardiac assistsystem is constructed of a primary device housing that has controlcircuitry therein. This control circuitry may include a control unitsuch a microprocessor or other logic circuits and digital signalprocessing circuits. The primary device housing may also include anoscillator, memory, filtering circuitry, an interface, sensors, a powersupply, and/or a light source. In a preferred embodiment, the controlcircuitry including the oscillator and an amplifier operate at anamplitude level above that of an induced signal from amagnetic-resonance imaging field.

[0344] The microprocessor may be an integrated circuit for controllingthe operations of the cardiac assist system. The microprocessorintegrated circuit can select a mode of operation for the cardiac assistsystem based on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

[0345] The primary device housing also can contain circuitry to detectand isolate crosstalk between device pulsing operations and devicesensing operations, a battery power source and a battery power sourcemeasuring circuit. In such an embodiment the microprocessor integratedcircuit can automatically adjust a value for determining an electivereplacement indication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

[0346] The microprocessor integrated circuit can be programmable from asource external of the cardiac assist system and can providephysiological or circuit diagnostics to a source external of the cardiacassist system.

[0347] The cardiac assist system also includes a lead system to transmitand receive signals between a heart and the primary device housing. Thelead system may be a fiber optic based communication system, preferablya fiber optic communication system contains at least one channel withina multifiber optic bundle, or the lead system may be a plurality ofelectrical leads. The lead system is coated with electromagneticinterference resistant material.

[0348] The cardiac assist system further includes a detection circuit.The detection circuit is located in the primary device housing anddetects an electromagnetic interference insult upon the cardiac assistsystem. Examples of such detection circuits are a thermistor heatdetector; a high frequency interference detector; a high voltagedetector; and/or an excess current detector. The control circuit placesthe cardiac assist system in an asynchronous mode upon detection of theelectromagnetic interference insult by the detection system.

[0349] With respect to the electrical lead system, the plurality ofelectrical leads has a second shielding therearound, the secondshielding preventing the electrical leads from conducting strayelectromagnetic interference. The second shielding can be a metallicsheath to prevent the electrical leads from conducting strayelectromagnetic interference; a carbon composite sheath to prevent theelectrical leads from conducting stray electromagnetic interference; ora polymer composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference. The electrical leads mayeither be unipolar, bipolar or a combination of the two. Moreover, thelead system itself may be a combination of fiber optic leads andelectrical leads wherein these electrical leads can be either unipolar,bipolar or a combination of the two.

[0350] The lead systems may include a sensing and stimulation system atan epicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

[0351] Although the leads may be fiber optic strands or electrical leadswith proper shielding, the actual interface to the tissue, theelectrodes, cannot be shielded because the tissue needs to receive thestimulation from the device without interference. This causes theelectrodes to be susceptible to electromagnetic interference or insult,and such insult can cause either damage to the tissue area or thecircuitry at the other end. To realize immunity from the electromagneticinterference or insult, each electrode has an anti-antenna geometricalshape. The anti-antenna geometrical shape prevents the electrode frompicking up and conducting stray electromagnetic interference.

[0352] Moreover, the primary device housing, may include for redundancyfiltering circuits as the ends of the electrical leads at the primaryhousing interface to remove stray electromagnetic interference from asignal being received from the electrical lead. The filters may becapacitive and inductive filter elements adapted to filter outpredetermined frequencies of electromagnetic interference.

[0353] The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

[0354] In addition to the electromagnetic interference shielding, theprimary device housing, and lead system, whether it is a fiber opticsystem or electrical lead system can be coated with a biocompatiblematerial. Such a biocompatible material is preferably a non-permeablediffusion resistant biocompatible material.

[0355] In a third embodiment of the present invention as illustrated inthe figures, a cardiac assist system includes a primary device housing.The primary device housing has a control circuit, therein, to performsynchronous cardiac assist operations. The cardiac assist system furtherincludes a secondary device housing that has a control circuit, therein,to perform asynchronous cardiac assist operations.

[0356] A detection circuit, located in either the primary or secondarydevice housing and communicatively coupled to the control circuits,detects an electromagnetic interference insult upon the cardiac assistsystem. The detection circuit can also be located in a third devicehousing. Examples of such detection circuits are a thermistor heatdetector; a high frequency interference detector; a high voltagedetector; and/or an excess current detector.

[0357] The detection circuit is communicatively coupled to the controlcircuits through a fiber optic communication system and/or throughelectromagnetic interference shielded electrical leads. The fiber opticcommunication system or the electromagnetic interference shieldedelectrical leads are coated with a biocompatible material.

[0358] The control circuit of the primary device housing terminatessynchronous cardiac assist operations and the control circuit of thesecondary device housing initiates asynchronous cardiac assistoperations upon detection of the electromagnetic interference insult bythe detection system. In this system the control circuit of thesecondary device housing places the cardiac assist system in theasynchronous mode for a duration of the electromagnetic interferenceinsult and terminates the asynchronous mode of the cardiac assist systemupon detection of an absence of an electromagnetic interference insultby the detection system. The control circuit of the primary devicehousing terminates the synchronous mode of the cardiac assist system forthe duration of the electromagnetic interference insult and re-initiatesthe synchronous mode of the cardiac assist system upon detection of anabsence of an electromagnetic interference insult by the detectionsystem.

[0359] The primary and secondary device housings have formed aroundthem, in a preferred embodiment, a shield. The shield can be formed ofvarious composite materials so as to provide an electromagnetic shieldaround the primary housing. Examples of such materials are metallicshielding or polymer or carbon composites such as carbon fullerenes.This shield or sheath around the primary device housing shields theprimary device housing and any circuits therein from electromagneticinterference.

[0360] In addition to the electromagnetic interference shielding, theprimary and secondary device housings are coated with a biocompatiblematerial. Such a biocompatible material is preferably a non-permeablediffusion resistant biocompatible material.

[0361] The cardiac assist system also includes a lead system to transmitand receive signals between heart and the primary and secondary devicehousings. The lead system may be a fiber optic based communicationsystem, preferably a fiber optic communication system contains at leastone channel within a multi-fiber optic bundle, or the lead system may bea plurality of electrical leads. The lead system is coated withelectromagnetic interference resistant material.

[0362] With respect to the electrical lead system, the plurality ofelectrical leads has a second shielding therearound, the secondshielding preventing the electrical leads from conducting strayelectromagnetic interference. The second shielding can be a metallicsheath to prevent the electrical leads from conducting strayelectromagnetic interference; a carbon composite sheath to prevent theelectrical leads from conducting stray electromagnetic interference; ora polymer composite sheath to prevent the electrical leads fromconducting stray electromagnetic interference. The electrical leads mayeither be unipolar, bipolar or a combination of the two. Moreover, thelead system itself may be a combination of fiber optic leads andelectrical leads wherein these electrical leads can be either unipolar,bipolar or a combination of the two.

[0363] The lead systems may include a sensing and stimulation system atan epicardial-lead interface with a desired anatomical cardiac tissueregion. The sensing and stimulation system may include optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region and/or electrical sensing components to detectphysiological signals from the desired anatomical cardiac tissue region.The sensing and stimulation system may also include optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region and/or electricalpulsing components to deliver a stimulus of a predetermined duration andpower to the desired anatomical cardiac tissue region. The sensing andstimulation system may also include hydrostatic pressure sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.

[0364] Although the leads may be fiber optic strands or electrical leadswith proper shielding, the actual interface to the tissue, theelectrodes, cannot be shielded because the tissue needs to receive thestimulation from the device without interference. This causes theelectrodes to be susceptible to electromagnetic interference or insult,and such insult can cause either damage to the tissue area or thecircuitry at the other end. To realize immunity from the electromagneticinterference or insult, each electrode has an anti-antenna geometricalshape. The anti-antenna geometrical shape prevents the electrode frompicking up and conducting stray electromagnetic interference.

[0365] In a fourth embodiment of the present invention, an implantablepacemaker or a cardiac assist system is used to regulate the heartbeatof a patient. The implantable cardiac assist system is constructed of aprimary device housing that has control circuitry therein. This controlcircuitry may include a control unit such a microprocessor or otherlogic circuits and digital signal processing circuits. The primarydevice housing may also include an oscillator, memory, filteringcircuitry, an interface, sensors, a power supply, and/or a light source.

[0366] The microprocessor may be an integrated circuit for controllingthe operations of the cardiac assist system. The microprocessorintegrated circuit can select a mode of operation for the cardiac assistsystem based on predetermined sensed parameters. In one embodiment, themicroprocessor integrated circuit isolates physiological signals usingan analog or digital noise filtering circuit.

[0367] The primary device housing also can contain circuitry to detectand isolate crosstalk between device pulsing operations and devicesensing operations, a battery power source and a battery power sourcemeasuring circuit. In such an embodiment the microprocessor integratedcircuit can automatically adjust a value for determining an electivereplacement indication condition of a battery power source. The value isautomatically adjusted by the microprocessor integrated circuit inresponse to a measured level of a state of the battery power source. Themeasured level is generated by the battery power source measuringcircuit that is connected to the battery power source.

[0368] The microprocessor integrated circuit can be programmable from asource external of the cardiac assist system and can providephysiological or circuit diagnostics to a source external of the cardiacassist system.

[0369] The microprocessor integrated circuit may also include adetection circuit to detect a phase timing of an externalelectromagnetic field. The microprocessor integrated circuit alters itsoperations to avoid interfering with the detected externalelectromagnetic field. Moreover, the cardiac assist system would includesensors may detect a heart signal and to produce a sensor signaltherefrom and a modulator to modulate the sensor signal to differentiatethe sensor signal from electromagnetic interference or a samplingcircuit to sample the sensor signal multiple times to differentiate thesensor signal from electromagnetic interference, undesirable acousticsignals, large muscle contractions, or extraneous infrared light.

[0370] The primary device housing has formed around it, in a preferredembodiment, a shield. The shield can be formed of various compositematerials so as to provide an electromagnetic shield around the primaryhousing. Examples of such materials are metallic shielding or polymer orcarbon composites such as carbon fullerenes. This shield or sheatharound the primary device housing shields the primary device housing andany circuits therein from electromagnetic interference.

[0371] The cardiac assist system also includes a fiber optic lead systemto transmit and receive signals between a heart and the primary devicehousing. The fiber optic communication system preferably contains atleast one channel within a multi-fiber optic bundle. The lead system canbe coated with electromagnetic interference resistant material.

[0372] The optic fiber lead systems may include a sensing andstimulation system at an epicardial-lead interface with a desiredanatomical cardiac tissue region. The sensing and stimulation system mayinclude optical sensing components to detect physiological signals fromthe desired anatomical cardiac tissue region and/or electrical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region (in the electrical sensing components, electricalpulses are converted to light pulses before being transmitted over thelead system). The sensing and stimulation system may also includeoptical pulsing components to deliver a stimulus of a predeterminedduration and power to the desired anatomical cardiac tissue regionand/or electrical pulsing components to deliver a stimulus of apredetermined duration and power to the desired anatomical cardiactissue region (in the electrical delivering components, light pulses areconverted to electrical pulses after the light pulses are received fromthe lead system). The sensing and stimulation system may also includehydrostatic pressure sensing components to detect physiological signalsfrom the desired anatomical cardiac tissue region.

[0373] Although the leads are fiber optic strands, the actual interfaceto the tissue, the electrodes, cannot be fiber optics because the tissueneeds to receive electrical stimulation from the device. This causes theelectrodes to be susceptible to electromagnetic interference or insult,and such insult can cause either damage to the tissue area or thecircuitry at the other end. To realize immunity from the electromagneticinterference or insult, each electrode has an anti-antenna geometricalshape. The anti-antenna geometrical shape prevents the electrode frompicking up and conducting stray electromagnetic interference.

[0374] In addition, the primary device housing and the fiber optic leadsystem are coated with a biocompatible material. Such a biocompatiblematerial is preferably a non-permeable diffusion resistant biocompatiblematerial. The primary device housing further includes an electronicsignal generator and a controlled laser light pulse generator linked tothe electronic signal generator. A fiber optic light pipe for receivesthe laser light pulse from the controlled laser light pulse generator ata proximal end of the fiber optic light pipe. A photodiode, at a distalend of the fiber optic light pipe converts the laser light pulse backinto an electrical pulse. The electrical pulse drives the cardiacelectrodes coupled to the photodiode and to a cardiac muscle.

[0375] In a fifth embodiment of the present invention as illustrated inthe figures, an implantable cable for transmission of a signal to andfrom a body tissue of a vertebrate is constructed of a fiber opticbundle having a cylindrical surface of non-immunogenic, physiologicallycompatible material. The fiber optic bundle is capable of beingpermanently implanted in a body cavity or subcutaneously. An opticalfiber in the fiber optic bundle has a distal end for implantation at oradjacent to the body tissue and a proximal end. The proximal end isadapted to couple to and direct an optical signal source. The distal endis adapted to couple to an optical stimulator. The optical fiberdelivers an optical signal intended to cause the optical stimulatorlocated at a distal end to deliver an excitatory stimulus to a selectedbody tissue. The stimulus causes the selected body tissue to function asdesired.

[0376] The optical stimulator is constructed, in a preferred embodiment,is constructed of a photoresponsive device for converting the lightreceived from the optical signal source into electrical energy and forsensing variations in the light energy to produce control signals. Acharge-accumulating device, such as a CCD, receives and stores theelectrical energy produced by the photoresponsive device. A dischargecontrol device, responsive to the control signals, directs the storedelectrical energy from the charge-accumulating device to the cardiacassist device associated with the heart.

[0377] A second optical fiber has a distal end coupled to a sensor and aproximal end coupled to a device responsive to an optical signaldelivered by the second optical fiber. The sensor generates an opticalsignal to represent a state of a function of the selected body tissue toprovide feedback to affect the activity of the optical signal source.

[0378] In a sixth embodiment of the present invention, an implantablephotonic cable system is constructed from a photonic cable, a lightsource and a light detector. The light source and the light detectorform an optical sensor unit. The photonic cable, in this embodiment,receives signals from a selected tissue area and delivering signals tothe selected tissue area. The system further includes transducers.

[0379] The light source illuminates a tissue area, and the lightdetector detects properties of the tissue by measuring the output of thelight signals reflective from the tissue area. A hollow porous cylinderis used to attach the optical sensor unit to the tissue area.Preferably, the light source is a light emitting diode and the lightdetector is a photodiode comprising multiple channels. The multiplechannels detect light emission at multiple wavelengths. Moreover, theoptical sensor unit includes either a pressure-optical transducer or areflective element mechanically driven by a moving part of the selectedbody tissue.

[0380] In a seventh embodiment of the present invention, a cardiacassist system is constructed of a primary device housing having acontrol circuit therein. A shielding is formed around the primary devicehousing to shield the primary device housing and any circuits thereinfrom electromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. A changingmagnetic field sensor to sense a change in magnetic field around theprimary housing. The switch places the control circuitry into afixed-rate mode of operation when the changing magnetic field sensorsenses a predetermined encoded changing magnetic field.

[0381] In another embodiment of the present invention, a method preventsa cardiac assist system from failing during magnetic resonance imaging.A magnetic-resonance imaging system determines a quiet period for acardiac assist system. Upon making this determination, themagnetic-resonance imaging system locks the timing of a magneticresonance imaging pulse to occur during a quiet period of the cardiacassist system.

[0382] In an eighth embodiment of the present invention, a cardiacassist system is constructed of a primary device housing having acontrol circuit therein. A shielding is formed around the primary devicehousing to shield the primary device housing and any circuits thereinfrom electromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. An acousticsensor senses a predetermined acoustic signal, and the switch places thecontrol circuitry into a fixed-rate mode of operation when the acousticsensor senses the predetermined acoustic signal.

[0383] In a ninth embodiment of the present invention, a cardiac assistsystem is constructed of a primary device housing having a controlcircuit therein. A shielding is formed around the primary device housingto shield the primary device housing and any circuits therein fromelectromagnetic interference. A lead system to transmit and receivesignals between a heart and the primary device housing. A switch placesthe control circuitry into a fixed-rate mode of operation. A nearinfrared sensor senses a predetermined near infrared signal. The switchplaces the control circuitry into a fixed-rate mode of operation whenthe near infrared sensor senses the predetermined near infrared signal.

[0384] The present invention also contemplates an electromagneticradiation immune tissue invasive stimulation system that includes aphotonic lead having a proximal end and a distal end; a light source, inthe proximal end of the photonic lead, to produce a first light having afirst wavelength; a wave-guide between the proximal end and distal endof the photonic lead; a distal sensor, in the distal end of the photoniclead, to convert the first light into electrical energy into controlsignals; an electrical energy storage device to store electrical energy;and a control circuit, in response to the control signals, to cause aportion of the stored electrical energy to be delivered to apredetermined tissue region. In this embodiment, the predeterminedtissue region may be, for example, a region of the spinal cord, a regionof the brain, a region associated with a deep brain structure, the vagalnerve, peripheral nerves that innervate muscles, sacral nerve roots toelicit functional contraction of muscles innervated by the sacral nerveroots, sacral nerve roots associated with bladder function, a region ofthe cochlea, a region of the stomach, or the hypoglossal nerve.

[0385] The present invention also contemplates an electromagneticradiation immune tissue invasive sensing system that includes a photoniclead having a proximal end and a distal end; a light source, in theproximal end of the photonic lead, to produce a first light having afirst wavelength; a wave-guide between the proximal end and distal endof the photonic lead; a distal sensor, in the distal end of the photoniclead, to convert the first light into electrical energy into controlsignals; an electrical energy storage device to store electrical energy;and a bio-sensor, in the distal end of the photonic lead, to sense acharacteristic of a predetermined tissue region. The light source, inthe proximal end of the photonic lead, produces a second light having asecond wavelength. The distal sensor, in the distal end of the photoniclead and responsive to the bio-sensor, reflects the second light backthe proximal end of the photonic lead such that a characteristic of thesecond light is modulated to encode the sensed characteristic of thepredetermined tissue region. In this embodiment, the sensedcharacteristic may be, for example, an ECG, an EKG, an esophageal ECG, alevel of oxygen, blood pressure, intracranial pressure, or temperature.

[0386] The present invention also contemplates an electromagneticradiation immune sensing system that includes a photonic lead having aproximal end and a distal end; a light source, in the proximal end ofthe photonic lead, to produce a first light having a first wavelengthand a second light having a second wavelength; a wave-guide between theproximal end and distal end of the photonic lead; a bio-sensor, in thedistal end of the photonic lead, to measure changes in an electric fieldlocated outside a body, the electric field being generated by theshifting voltages on a body's skin surface; and a distal sensor, in thedistal end of the photonic lead, to convert the first light intoelectrical energy and, responsive to the bio-sensor, to reflect thesecond light back the proximal end of the photonic lead such that acharacteristic of the second light is modulated to encode the measuredchanges in the electric field. In this embodiment, the measured electricfield may correspond to an ECG signal. Also in this embodiment, thebio-sensor has impedance higher than an impedance of an air gap betweenthe bio-sensor and the body.

[0387] While various examples and embodiments of the present inventionhave been shown and described, it will be appreciated by those skilledin the art that the spirit and scope of the present invention are notlimited to the specific description and drawings herein, but extend tovarious modifications and changes all as set forth in the followingclaims.

What is claimed is:
 1. A cardiac assist system, comprising: a primarydevice housing; and said primary device housing having a control circuittherein; a lead system to transmit and receive signals between a desiredanatomical cardiac tissue region and said primary device housing; saidlead system including a sensing and stimulation system at anepicardial-lead interface with the desired anatomical cardiac tissueregion; said sensing and stimulation system including optical sensingcomponents to detect physiological signals from the desired anatomicalcardiac tissue region.
 2. The cardiac assist system as claimed in claim1, wherein said sensing and stimulation system includes optical pulsingcomponents to deliver a stimulus of a predetermined duration and powerto the desired anatomical cardiac tissue region.
 3. The cardiac assistsystem as claimed in claim 1, wherein said optical sensing componentsdetect physiological signals by measuring a displacement of a mirror. 4.The cardiac assist system as claimed in claim 1, wherein said opticalsensing components detect physiological signals by measuring a change ina refractive index of a section of cladding.
 5. The cardiac assistsystem as claimed in claim 1, wherein said optical sensing component isan optical strain gauge to detect physiological signals.
 6. The cardiacassist system as claimed in claim 1, wherein said optical sensingcomponent is an optical-pressure sensor to detect physiological signals.7. The cardiac assist system as claimed in claim 2, wherein said opticalsensing components detect physiological signals by measuring adisplacement of a mirror.
 8. The cardiac assist system as claimed inclaim 2, wherein said optical sensing components detect physiologicalsignals by measuring a change in a refractive index of a section ofcladding.
 9. The cardiac assist system as claimed in claim 2, whereinsaid optical sensing component is an optical strain gauge to detectphysiological signals.
 10. The cardiac assist system as claimed in claim2, wherein said optical sensing component is an optical-pressure sensorto detect physiological signals.
 11. The cardiac assist system asclaimed in claim 1, wherein said primary device housing further includesan electronic signal generator and a controlled laser light pulsegenerator linked to said electronic signal generator and said leadsystem is a fiber optic lead system; said fiber optic based lead systemincluding a fiber optic light pipe for receiving the laser light pulsefrom said controlled laser light pulse generator at a proximal end ofsaid fiber optic light pipe, said sensing and stimulation systemincluding a photodiode, coupled to a distal end of said fiber opticlight pipe, to convert the laser light pulse back into an electricalpulse and electrically driven cardiac electrodes coupled to saidphotodiode and the desired anatomical cardiac tissue region.
 12. Thecardiac assist system as claimed in claim 1, wherein said lead systemcomprises a photonic cable; and said sensing and stimulation systemincluding a light source and a light detector, said light source andsaid light detector forming the optical sensing component to detectphysiological signals from the desired anatomical cardiac tissue region;said photonic cable receiving signals from the desired anatomicalcardiac tissue region and delivering signals to the desired anatomicalcardiac tissue region.
 13. The cardiac assist system as claimed in claim12, wherein said light source illuminates the desired anatomical cardiactissue region and said light detector detects properties of the desiredanatomical cardiac tissue region by measuring the output of the lightsignals reflective from the desired anatomical cardiac tissue region.14. The cardiac assist system as claimed in claim 13, wherein said lightsource is a light emitting diode and said light detector is a photodiodecomprising multiple channels.
 15. The cardiac assist system as claimedin claim 14, wherein said multiple channels detect light emission atmultiple wavelengths.
 16. The cardiac assist system as claimed in claim12, wherein the optical sensing component includes a pressure-opticaltransducer.
 17. The cardiac assist system as claimed in claim 12,wherein the optical sensing component includes a reflective elementmechanically driven by a moving part of the desired anatomical cardiactissue region.
 18. A tissue invasive device, comprising: a primarydevice housing; and said primary device housing having a control circuittherein; a lead system to transmit and receive signals between aselected tissue region and said primary device housing; said lead systemincluding a sensing and stimulation system at an interface with theselected tissue region; said sensing and stimulation system includingoptical sensing components to detect physiological signals from theselected tissue region.
 19. The tissue invasive device as claimed inclaim 18, wherein said sensing and stimulation system includes opticalpulsing components to deliver a stimulus of a predetermined duration andpower to the selected tissue region.
 20. The tissue invasive device asclaimed in claim 18, wherein said optical sensing components detectphysiological signals by measuring a displacement of a mirror.
 21. Thetissue invasive device as claimed in claim 18, wherein said opticalsensing components detect physiological signals by measuring a change ina refractive index of a section of cladding.
 22. The tissue invasivedevice as claimed in claim 18, wherein said optical sensing component isan optical strain gauge to detect physiological signals.
 23. The tissueinvasive device as claimed in claim 18, wherein said optical sensingcomponent is an optical-pressure sensor to detect physiological signals.24. The tissue invasive device as claimed in claim 19, wherein saidoptical sensing components detect physiological signals by measuring adisplacement of a mirror.
 25. The tissue invasive device as claimed inclaim 19, wherein said optical sensing components detect physiologicalsignals by measuring a change in a refractive index of a section ofcladding.
 26. The tissue invasive device as claimed in claim 19, whereinsaid optical sensing component is an optical strain gauge to detectphysiological signals.
 27. The tissue invasive device as claimed inclaim 19, wherein said optical sensing component is an optical-pressuresensor to detect physiological signals.
 28. The tissue invasive deviceas claimed in claim 18, wherein said primary device housing furtherincludes an electronic signal generator and a controlled laser lightpulse generator linked to said electronic signal generator and said leadsystem is a fiber optic lead system; said fiber optic based lead systemincluding a fiber optic light pipe for receiving the laser light pulsefrom said controlled laser light pulse generator at a proximal end ofsaid fiber optic light pipe, said sensing and stimulation systemincluding a photodiode, coupled to a distal end of said fiber opticlight pipe, to convert the laser light pulse back into an electricalpulse and electrically driven cardiac electrodes coupled to saidphotodiode and the selected tissue region.
 29. The tissue invasivedevice as claimed in claim 18, wherein said lead system comprises aphotonic cable; and said sensing and stimulation system including alight source and a light detector, said light source and said lightdetector forming the optical sensing component to detect physiologicalsignals from the selected tissue region; said photonic cable receivingsignals from the selected tissue region and delivering signals to theselected tissue region.
 30. The tissue invasive device as claimed inclaim 29, wherein said light source illuminates the selected tissueregion and said light detector detects properties of the selected tissueregion by measuring the output of the light signals reflective from theselected tissue region.
 31. The tissue invasive device as claimed inclaim 30, wherein said light source is a light emitting diode and saidlight detector is a photodiode comprising multiple channels.
 32. Thetissue invasive device as claimed in claim 31, wherein said multiplechannels detect light emission at multiple wavelengths.
 33. The tissueinvasive device as claimed in claim 29, wherein the optical sensingcomponent includes a pressure-optical transducer.
 34. The tissueinvasive device as claimed in claim 29, wherein the optical sensingcomponent includes a reflective element mechanically driven by a movingpart of the selected tissue region.